Win32/Parite is a packed, encrypted virus that infects files on the local file system and on writeable network shares. The virus repeatedly performs a sequence whereby it selects an .exe or .scr executable file, infects the file, waits a random time interval, selects and infects another file, and so on.
To each file that it selects for infection, the virus appends a new code section named ".<three random alphabetic characters>", such as .mpg. The virus changes the code-entry point of the file to the new, appended section. The virus contains certain code that it unpacks, re-encrypts, re-packs, and then copies to the new section of the executable file. This copied code consists of certain DLL code and some additional execution instructions.
When a file infected in this way runs, the execution instructions in the appended section of the file unpack and decrypt the DLL code in the appended section and drop it as a new file into the Windows temporary directory. The name of the dropped DLL consists of 4 randomly-chosen alphanumeric characters: the first three characters are alphabetic and the final character is a digit. Although the file is actually a DLL, the file extension is .tmp. So for example, the file could have a name like fia1.tmp.
The virus may also creates a marker in the registry:
Adds value: PINF
To subkey: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer
This value contains the full path to the dropped DLL. Win32/Parite may check for this registry entry to determine whether the virus is already running on the computer.
The execution instructions in the appended section of the infected file load the dropped DLL. The DLL exports a start function which contains the main virus code. The virus code calls the start function, which injects the DLL into the explorer.exe process. When a certain condition is satisfied, the DLL code runs and infects other .exe and .scr executable files.
Win32/Parite does not run executable files that it infects. When an infected file runs (for example, when a user or the system runs the file), the virus code in the appended section runs and then returns control to the original code-entry point of the executable file. The executable file then runs normally even though it is infected, so there may be no readily apparent indication to a user of any malicious activity.
Take the following steps to help prevent infection on your system:
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Enable a firewall on your computer.
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Get the latest computer updates.
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Use up-to-date antivirus software.
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Use caution with attachments and file transfers.
Enable a firewall on your computer
Use a third-party firewall product or turn on the Microsoft Windows XP Internet Connection Firewall.
To turn on the Internet Connection Firewall in Windows XP
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Click Start, and click Control Panel.
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Click Network and Internet Connections. If you do not see Network and Internet Connections, click Switch to Category View.
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Click Change Windows Firewall Settings.
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Select On.
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Click OK.
Get the latest computer updates
Updates help protect your computer from viruses, worms, and other threats as they are discovered. You can use the Automatic Updates feature in Windows XP to automatically download future Microsoft security updates while your computer is on and connected to the Internet.
To turn on Automatic Updates in Windows XP
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Click Start, and click Control Panel.
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Click System.
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Click Automatic Updates.
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Select a setting. Microsoft recommends selecting Automatic. If you do not choose Automatic, but you choose to be notified when updates are ready, a notification balloon appears when new downloads are available to install. Click the notification balloon to review and install the updates.
Use up-to-date antivirus software
Most antivirus software can detect and prevent infection by known malicious software. To help protect you from infection, you should always run antivirus software that is updated with the latest signature files. Antivirus software is available from several sources. For more information, see http://www.microsoft.com/athome/security/downloads/default.mspx
Use caution with attachments and file transfers
Exercise caution with e-mail and attachments received from unknown sources, or received unexpectedly from known sources. Use extreme caution when accepting file transfers from known or unknown sources.
