MS06-016 is not categorized as virus, worm, Trojan or backdoor. It is an important vulnerability in Outlook Express running on Windows 2003/XP/2000 computers, which allows arbitrary code to be remotely executed in the vulnerable computer. Affected versions of Outlook Express are 5.5 and 6.
If exploited successfully, MS06-016 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.
This vulnerability is usually exploited by sending a specially crafted WAB file to users or hosting a malicious WAB file in a web page, and then enticing them into saving it to the Desktop and opening it with Outlook Express.
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. However, provided that this is a cumulative patch, make sure that you download the latest security patch available.