Nurech.B is a computer worm that infects computers through MSN Messenger. It inserts a link in the chat window while you are chatting with someone, thus making it look as if your friend sent it and thus exploiting that trust. Once you click on that link, it downloads an .exe file with a name such a "Valentine Card" or "Happy Valentine's Day". Once infected, it spreads through your MSN to your friends and is invisible.
The virus disables virus scanners and access to the folders containing any antivirus software. It adds keys to the registry as well, and therefore you won't be allowed to access the registry either. You cannot get rid of it from the registry using registry cleaning software because it has a rootkit function that allows it to hide its key in the registry and also its processes thus making it virtually invisible. Many people head to Google to search for an antivirus software but any search for terms such as virus, spyware, malware etc. closes the browser.