MS09-041 is not categorized as virus, worm, Trojan or backdoor. It is an important vulnerability in the Windows Workstation Service on Windows 2008/Vista/2003/XP, which allows to gain local privilege escalation.
The Workstation service supports the routing of remote file and network print resource requests.
If exploited successfully, MS09-041 allows to gain unauthorized privileges on a computer or network. An example of privilege elevation would be an unprivileged user who could manage to be added to the Administrator's 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 creating a specially crafted RPC message and sending it to an affected system.
If you have a Windows 2008/Vista/2003/XP computer, it is recommended to download and apply the security patch for this vulnerability. Access the web page for downloading the patch.