System Alert blinking in task bar...HELP!

When I click on this annoying alert it states virus activities detected and it then sends me directly to ANTIVERMINS website. Can't get on the internet but this site pops up instantly. I did not attempt the free scan as I did a web search and some sites stated that it's a hoax site and they offer links to remove the ANTIVERMINS link. I didn't bother to do that either as I need a trustworthy link.

 

I'm currently using Webroot Spy Sweeper with Antivirus. I've done several sweeps and noticed TROJAN HORSE FOUND. I removed it.

 

What further steps do I need to take?

 

Thanks for your help :o)