MS05-008 is not categorized as virus, worm, Trojan or backdoor. It is an important vulnerability in computers with Windows 2003/XP/2000.
MS05-008 is exploited by creating a specially crafted web page and then persuading users to visit that site. If the user took certain actions on that Web page, executable files of the attacker's choice could be saved in locations specified by the hacker on the user's system, without requesting approval for the download. It can also be exploited through HTML malicious e-mail messages.
Although this code could not be run through MS05-008 directly, the operating system might open the file if it is saved to a sensitive location (for example the Windows startup directory), or a user may open the file inadvertently and cause the attacker's code to run.
Running that code 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.
Remember that user interaction is required to exploit this vulnerability.
If you have any of the vulnerable systems installed on your computer, it is recommendable to download and apply the security patches for this vulnerability, available through Microsoft Security bulletins MS05-008 and MS05-008. Take in mind that it is necessary to install both parches in order to succesfully avoid this vulnerability.