Normally you don't need to erase your disk to reinstall OS X. The OS X Installer is designed to allow you to perform an install in place if you are troubleshooting. If you need to erase your disk because you are transferring your computer to a new owner, you can use Disk Utility to erase the disk before reinstalling. 

Important: Before you erase and reinstall, back up your essential files. If you’re installing on a notebook computer, make sure your power adapter is connected and plugged in.

Use these steps if you need to erase a disk before installing OS X:

1. Before you begin, you need to be connected to the Internet.
2. Choose Apple menu > Restart, and then hold down the Command (⌘) and R keys while the computer restarts.
3. Select “Disk Utility,” and then click Continue.
4. Select your startup disk from the list on the left, and then click the Erase tab.
5. From the Format pop-up menu, select Mac OS Extended (Journaled), type a name for your disk, and then click Erase.
6. After the disk has been erased, choose Disk Utility > Quit Disk Utility.
7. If you’re not connected to the Internet, choose a network from the Wi-Fi menu in the right corner of the menu bar (in the top-right corner of the screen).
8. Select Reinstall Mac OS X, click Continue, and then follow the instructions.

Open the section below for the kind of content you want to delete.

Apps

Audiobooks

Books

iTunes U courses

Mac Apps

Magazines and newspapers

Movies

Movie rentals

Music

Music videos

Ringtones/Tones

TV shows

For the protection of our customers, Apple does not disclose, discuss, or confirm security issues until a full investigation has occurred and any necessary patches or releases are available. To learn more about Apple Product Security, see the Apple Product Security website.

For information about the Apple Product Security PGP Key, see "How to use the Apple Product Security PGP Key."

Where possible, CVE IDs are used to reference the vulnerabilities for further information.

To learn about other Security Updates, see "Apple Security Updates".

Xcode 5.0

• Git

  Available for: OS X Mountain Lion v10.8.4 or later

  Impact: An attacker with a privileged network position may intercept user credentials or other sensitive information

  Description: When using the imap-send command, git did not verify that the server hostname matched a domain name in the X.509 certificate, which allowed a man-in-the-middle attacker to spoof SSL servers via an arbitrary valid certificate. This issue was addressed by updating git to version 1.8.3.1.

  CVE-ID

  CVE-2013-0308

For the protection of our customers, Apple does not disclose, discuss, or confirm security issues until a full investigation has occurred and any necessary patches or releases are available. To learn more about Apple Product Security, see the Apple Product Security website.

For information about the Apple Product Security PGP Key, see "How to use the Apple Product Security PGP Key."

Where possible, CVE IDs are used to reference the vulnerabilities for further information.

To learn about other Security Updates, see "Apple Security Updates".

OS X Server v2.2.2

• ClamAV

  Available for: OS X Mountain Lion v10.8 or later

  Impact: Multiple vulnerabilities in ClamAV

  Description: Multiple vulnerabilities existed in ClamAV, the most serious of which may lead to arbitrary code execution. This update addresses the issues by updating ClamAV to version 0.97.8.

  CVE-ID

  CVE-2013-2020

  CVE-2013-2021

• PostgreSQL

  Available for: OS X Mountain Lion v10.8 or later

  Impact: Multiple vulnerabilities in PostgreSQL

  Description: Multiple vulnerabilities existed in PostgreSQL, the most serious of which may lead to data corruption or privilege escalation. This update addresses the issues by updating PostgreSQL to version 9.2.4

  CVE-ID

  CVE-2013-1899

  CVE-2013-1900

  CVE-2013-1901

• Wiki Server

  Available for: OS X Mountain Lion v10.8 or later

  Impact: Multiple vulnerabilities in Wiki Server

  Description: Multiple cross-site scripting issues existed in Wiki Server. These issues were addressed by improved encoding of HTML output.

  CVE-ID

  CVE-2013-1034 : David Hoyt of Hoyt LLC Research

The OS X Mountain Lion v10.8.5 Update is recommended for all OS X Mountain Lion users.

Updating your system

1. You should back up your system before installation. To do this you can use Time Machine.
2. Do not interrupt the installation process once you have started to update your system.
3. You may experience unexpected results if you have third-party system software modifications installed, or if you've modified the operating system through other means.
4. Choose Apple menu () > Software Update to check for the latest Apple software via the Mac App Store, including this update.
5. Other software updates available for your computer may appear, which you should install. Note that an update's size may vary from computer to computer when installed using Software Update. Also, some updates must be installed prior to others.

You can also download the manual update installer. This is a useful option when you need to update multiple computers but only want to download the update once. These versions of the standalone installers are available from Apple Support Downloads. 

About the update

The OS X Mountain Lion v10.8.5 Update is recommended for all OS X Mountain Lion users. It improves the stability, compatibility, and security of your Mac. This update:

• Fixes an issue that may prevent Mail from displaying messages
• Improves AFP file transfer performance over 802.11ac Wi-Fi
• Resolves an issue that may prevent a screen saver from starting automatically
• Improves Xsan reliability
• Improves reliability when transferring large files over Ethernet
• Improves performance when authenticating to an Open Directory server
• Addresses an issue that prevented a smart card from unlocking preference panes in System Preferences
• Contains the improvements included in MacBook Air (Mid 2013) Software Update 1.0

These can be downloaded and installed via Software Update preferences, or from Apple Downloads.

For the protection of our customers, Apple does not disclose, discuss, or confirm security issues until a full investigation has occurred and any necessary patches or releases are available. To learn more about Apple Product Security, see the Apple Product Security website.

For information about the Apple Product Security PGP Key, see "How to use the Apple Product Security PGP Key."

Where possible, CVE IDs are used to reference the vulnerabilities for further information.

To learn about other Security Updates, see "Apple Security Updates". 

OS X Mountain Lion v10.8.5 and Security Update 2013-004

• Apache

  Available for: Mac OS X v10.6.8, Mac OS X Server v10.6.8, OS X Lion v10.7.5, OS X Lion Server v10.7.5, OS X Mountain Lion v10.8 to v10.8.4

  Impact: Multiple vulnerabilities in Apache

  Description: Multiple vulnerabilities existed in Apache, the most serious of which may lead to cross-site scripting. These issues were addressed by updating Apache to version 2.2.24.

  CVE-ID

  CVE-2012-0883

  CVE-2012-2687

  CVE-2012-3499

  CVE-2012-4558

• Bind

  Available for: OS X Lion v10.7.5, OS X Lion Server v10.7.5, OS X Mountain Lion v10.8 to v10.8.4

  Impact: Multiple vulnerabilities in BIND

  Description: Multiple vulnerabilities existed in BIND, the most serious of which may lead to a denial of service. These issues were addressed by updating BIND to version 9.8.5-P1. CVE-2012-5688 did not affect Mac OS X v10.7 systems.

  CVE-ID

  CVE-2012-3817

  CVE-2012-4244

  CVE-2012-5166

  CVE-2012-5688

  CVE-2013-2266

• Certificate Trust Policy

  Available for: Mac OS X 10.6.8, Mac OS X Server 10.6.8, OS X Lion v10.7.5, OS X Lion Server v10.7.5, OS X Mountain Lion v10.8 to v10.8.4

  Impact: Root certificates have been updated

  Description: Several certificates were added to or removed from the list of system roots. The complete list of recognized system roots may be viewed via the Keychain Access application.

• ClamAV

  Available for: Mac OS X 10.6.8, Mac OS X Server 10.6.8, OS X Lion v10.7.5, OS X Lion Server v10.7.5

  Impact: Multiple vulnerabilities in ClamAV

  Description: Multiple vulnerabilities exist in ClamAV, the most serious of which may lead to arbitrary code execution. This update addresses the issues by updating ClamAV to version 0.97.8.

  CVE-ID

  CVE-2013-2020

  CVE-2013-2021

• CoreGraphics

  Available for: OS X Mountain Lion v10.8 to v10.8.4

  Impact: Viewing a maliciously crafted PDF file may lead to an unexpected application termination or arbitrary code execution

  Description: A buffer overflow existed in the handling of JBIG2 encoded data in PDF files. This issue was addressed through additional bounds checking.

  CVE-ID

  CVE-2013-1025 : Felix Groebert of the Google Security Team

• ImageIO

  Available for: OS X Mountain Lion v10.8 to v10.8.4

  Impact: Viewing a maliciously crafted PDF file may lead to an unexpected application termination or arbitrary code execution

  Description: A buffer overflow existed in the handling of JPEG2000 encoded data in PDF files. This issue was addressed through additional bounds checking.

  CVE-ID

  CVE-2013-1026 : Felix Groebert of the Google Security Team

• Installer

  Available for: OS X Lion v10.7.5, OS X Lion Server v10.7.5, OS X Mountain Lion v10.8 to v10.8.4

  Impact: Packages could be opened after certificate revocation

  Description: When Installer encountered a revoked certificate, it would present a dialog with an option to continue. The issue was addressed by removing the dialog and refusing any revoked package.

  CVE-ID

  CVE-2013-1027

• IPSec

  Available for: Mac OS X 10.6.8, Mac OS X Server 10.6.8, OS X Lion v10.7.5, OS X Lion Server v10.7.5, OS X Mountain Lion v10.8 to v10.8.4

  Impact: An attacker may intercept data protected with IPSec Hybrid Auth

  Description: The DNS name of an IPSec Hybrid Auth server was not being matched against the certificate, allowing an attacker with a certificate for any server to impersonate any other. This issue was addressed by properly checking the certificate.

  CVE-ID

  CVE-2013-1028 : Alexander Traud of www.traud.de

• Kernel

  Available for: OS X Mountain Lion v10.8 to v10.8.4

  Impact: A local network user may cause a denial of service

  Description: An incorrect check in the IGMP packet parsing code in the kernel allowed a user who could send IGMP packets to the system to cause a kernel panic. The issue was addressed by removing the check.

  CVE-ID

  CVE-2013-1029 : Christopher Bohn of PROTECTSTAR INC.

• Mobile Device Management

  Available for: OS X Lion v10.7.5, OS X Lion Server v10.7.5, OS X Mountain Lion v10.8 to v10.8.4

  Impact: Passwords may be disclosed to other local users

  Description: A password was passed on the command-line to mdmclient, which made it visible to other users on the same system. The issue was addressed by communicating the password through a pipe.

  CVE-ID

  CVE-2013-1030 : Per Olofsson at the University of Gothenburg

• OpenSSL

  Available for: Mac OS X 10.6.8, Mac OS X Server 10.6.8, OS X Lion v10.7.5, OS X Lion Server v10.7.5, OS X Mountain Lion v10.8 to v10.8.4

  Impact: Multiple vulnerabilities in OpenSSL

  Description: Multiple vulnerabilities existed in OpenSSL, the most serious of which may lead to disclosure of user data. These issues were addressed by updating OpenSSL to version 0.9.8y.

  CVE-ID

  CVE-2012-2686

  CVE-2013-0166

  CVE-2013-0169

• PHP

  Available for: Mac OS X 10.6.8, Mac OS X Server 10.6.8, OS X Lion v10.7.5, OS X Lion Server v10.7.5, OS X Mountain Lion v10.8 to v10.8.4

  Impact: Multiple vulnerabilities in PHP

  Description: Multiple vulnerabilities existed in PHP, the most serious of which may lead to arbitrary code execution. These issues were addressed by updating PHP to version 5.3.26.

  CVE-ID

  CVE-2013-1635

  CVE-2013-1643

  CVE-2013-1824

  CVE-2013-2110

• PostgreSQL

  Available for: OS X Lion v10.7.5, OS X Lion Server v10.7.5, OS X Mountain Lion v10.8 to v10.8.4

  Impact: Multiple vulnerabilities in PostgreSQL

  Description: Multiple vulnerabilities exist in PostgreSQL, the most serious of which may lead to data corruption or privilege escalation. CVE-2013-1901 does not affect OS X Lion systems. This update addresses the issues by updating PostgreSQL to version 9.1.9 on OS X Mountain Lion systems, and 9.0.4 on OS X Lion systems.

  CVE-ID

  CVE-2013-1899

  CVE-2013-1900

  CVE-2013-1901

• Power Management

  Available for: OS X Mountain Lion v10.8 to v10.8.4

  Impact: The screen saver may not start after the specified time period

  Description: A power assertion lock issue existed. This issue was addressed through improved lock handling.

  CVE-ID

  CVE-2013-1031

• QuickTime

  Available for: Mac OS X 10.6.8, Mac OS X Server 10.6.8, OS X Lion v10.7.5, OS X Lion Server v10.7.5, OS X Mountain Lion v10.8 to v10.8.4

  Impact: Viewing a maliciously crafted movie file may lead to an unexpected application termination or arbitrary code execution

  Description: A memory corruption issue existed in the handling of 'idsc' atoms in QuickTime movie files. This issue was addressed through additional bounds checking.

  CVE-ID

  CVE-2013-1032 : Jason Kratzer working with iDefense VCP

• Screen Lock

  Available for: OS X Mountain Lion v10.8 to v10.8.4

  Impact: A user with screen sharing access may be able to bypass the screen lock when another user is logged in

  Description: A session management issue existed in the screen lock's handling of screen sharing sessions. This issue was addressed through improved session tracking.

  CVE-ID

  CVE-2013-1033 : Jeff Grisso of Atos IT Solutions, Sébastien Stormacq

• sudo

  Available for: OS X Lion v10.7.5, OS X Lion Server v10.7.5, OS X Mountain Lion v10.8 to v10.8.4

  Impact: An attacker with control of an admin user's account may be able to gain root privileges without knowing the user's password

  Description: By setting the system clock, an attacker may be able to use sudo to gain root privileges on systems where sudo has been used before. On OS X, only admin users can change the system clock. This issue was addressed by checking for an invalid timestamp.

  CVE-ID

  CVE-2013-1775

• Note: OS X Mountain Lion v10.8.5 also addresses an issue in which certain Unicode strings could cause applications to unexpectedly quit.

For the protection of our customers, Apple does not disclose, discuss, or confirm security issues until a full investigation has occurred and any necessary patches or releases are available. To learn more about Apple Product Security, see the Apple Product Security website.

For information about the Apple Product Security PGP Key, see "How to use the Apple Product Security PGP Key."

Where possible, CVE IDs are used to reference the vulnerabilities for further information.

To learn about other Security Updates, see "Apple Security Updates".

• JavaScriptCore

  Available for: Mac OS X v10.6.8, Mac OS X Server v10.6.8

  Impact: Visiting a maliciously crafted website may lead to an unexpected application termination or arbitrary code execution

  Description: Multiple memory corruption issues existed in JavaScriptCore's JSArray::sort() method. These issues were addressed through additional bounds checking.

  CVE-ID

  CVE-2012-3748 : Joost Pol and Daan Keuper of Certified Secure working with HP TippingPoint's Zero Day Initiative

  CVE-2013-0997 : Vitaliy Toropov working with HP's Zero Day Initiative

Using Network Utility

You can view the following information for each network connection from the Info tab:

• hardware address of the interface
• the current IP addresses assigned to the interface
• hardware speed and status (active or inactive)
• the name of the interface manufacturer and model (such as for an add-on PCI card in a Mac Pro or a connected USB to Ethernet adapter)
• a count of data packets sent and received over the interface
• a count of transmission errors and collisions on a connection

Network Utility also provides graphic user interface (GUI) methods for common command-line diagnostic tools, including:

Netstat Ping Lookup Traceroute Whois Finger Port Scan

To learn more about each of these tools and their uses, open Network Utility and select Network Utility Help from the Help menu. 

You can use this information, together with network information provided by the Network pane of System preferences, to investigate your network connection.

Locating Network Utility

Use these steps to locate and open the Network Utility app on your computer.

Snow Leopard, Lion, and Mountain Lion

 In OS X Mountain Lion and earlier, Network Utility is located in the Utilities folder of the Applications folder.

• From the Finder, choose Go > Utilities to go directly to the Utilities folder.