MS05-017 is not categorized as virus, worm, Trojan or backdoor. It is a vulnerability rated as important on Windows 2003/XP/2000/98 computers, which allows arbitrary code to be remotely executed in the vulnerable computer.
If exploited successfully, MS05-017 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.
MS05-017 is exploited by creating a specially crafted message and sending it to a vulnerable system.
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.
Though this vulnerability also affects Windows 98 computers, as it is not rated as critical, Microsoft has released no security patch for these systems, due to the end of support cycle for these operating systems.