MS06-011 is not categorized as virus, worm, Trojan or backdoor. It is an important vulnerability in Permissive Windows Services DACLs on Windows 2003/XP computers, which allows to perform a local privilege escalation attack in the vulnerable computer.
The acronym of DACL is Discretionary Access Control List.
If exploited successfully, MS06-011 allows hackers to gain unauthorized privileges on a computer or network. An example of privilege escalation would be an unprivileged user who could manage to be added to the Administrators' group. In such case, 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 running a specially crafted application in the vulnerable computer. However, the attacking user must have valid logon credentials (username and password).
If you have a Windows 2003/XP 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.