I have the exact same problem. The internet browser works for a short time then quits if you don't respond to the fake security alert. The initial home page address does not change, but every time you open firefox it automatically brings you to a page that says:
"

Insecure Internet activity. Threat of virus attack
_______________________________________________________________
Due to the insecure Internet browsing your PC can easily get infected with viruses, worms and trojans without your
knowledge, and can lead to system slowdown, freezes and crashes.
Also insecure Internet activity can result in revealing your personal information.
To get full advanced real-time protection for PC and Internet activity, register your antivirus software.
We recommend you protect your PC now and continue safe Internet browsing.
*Click here to get full advanced real-time protection and continue browsing
*Continue to this website unprotected (not recommended)
"
My internet is useless now, and I have to use a different computer to get to this page. AVG and Mcafee have both failed to prevent or detect this virus. I was able to download and run (with a lot of crashing) superAntiSpyware which detected about 27 threats, which I quarantined and deleted, but this has done nothing. I am running windows XP.
any help would be greatly greatly appreciated!