MS05-031 is not categorized as virus, worm, Trojan or backdoor. It is an important vulnerability in Step-by-Step Interactive Training on Windows 2003/XP/2000 computers, which allows to remotely execute arbitrary code in the vulnerable computer.
If exploited successfully, MS05-031 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.
MS05-031 is exploited by creating a specially crafted file. Then, it can be hosted in a malicious website that opens the file when accessed, or sent as an email attachment in a email message that entices users into opening it. However, keep in mind that user interaction is required to exploit this vulnerability.
If you have a Windows 2003/XP/2000 computer, it is recommendable to download and apply the security patch for this vulnerability. Click here to access the web page for downloading the patch.