MS07-051 is not categorized as virus, worm, Trojan or backdoor. It is a critical vulnerability in Microsoft Agent on Windows 2000 Service pack 4 computers, which allows arbitrary code to be remotely executed in the vulnerable computer.
Microsoft Agent is a software technology that allows users to learn how to use the computer easily.
If exploited successfully, MS07-051 allows hackers to gain remote control of the affected computer with the same privileges as the logged on user. If this user had administrator rights, the hacker could take complete control of the system: create, modify or delete files, install programs, create new user accounts, etc.
This vulnerability is usually exploited by hosting a malicious web page and enticing users into accessing it.
If you have a Windows 2000 Service pack 4 computer, it is recommended to download and apply the security patch for this vulnerability. Click here to access the web page for downloading the patch.
Bear in mind that this patch replaces a previous one, called MS07-020.