MS07-019 is not categorized as virus, worm, Trojan or backdoor. It is a critical vulnerability in the Universal Plug and Play (PnP) service in Windows XP, which allows arbitrary code to be remotely executed in the vulnerable computer.
If exploited successfully, MS07-019 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 exploited by sending an specially crafted HTTP request. However, this request must be sent by a user on the same subnet. Additionally, though attacks can be launched across the Internet, a firewall could be used in order to prevent those attacks.
If you have a Windows 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.