MS05-030 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, MS05-030 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 convincing users to configure Outlook Express to connect to a malicious NNTP server, or by compromising an existing NNTP server. The attacking user could then create a specially crafted response and send it to the vulnerable computer.
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.