MS06-046 is not categorized as virus, worm, Trojan or backdoor. It is a critical vulnerability in HTML Help ActiveX control on Windows 2003/XP/2000 computers, which allows to remotely execute arbitrary code in the vulnerable computer.
If exploited successfully, MS06-046 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 creating a specially crafted web page, and enticing users into accessing it.
Attacks can be launched across the Internet, but a firewall could be used in order to prevent those attacks.
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.
Additionally, bear in mind that this security bulletin replaces the previous bulletin, called MS05-001.