When it takes over your system, In the last week two of my laptops have become victims of this scam. You download a file in which you know and trust e.g. adobe shockwave player only to find that its an advertisment for an antivirus program that won't let you connect to the internet and tells you that your whole system is infected with every known virus, trojan, etc known to exist so shuts down any window in windows Vista you open.
It disrupts you internet connection by changing you proxy server settings and sets it so you can only visit its webpage to purchase the so called advertised product. The website it makes you visit is www.antivirdial.com and the product it attempts to get you to purchase is Security Suite I have just done a system restore to get rid of it.
I attempted to go to the so called products website and it is a reported unsafe website. So all that can be said is be careful what you download.
If you happen to be taken over by this do a system restore and then open a web page and go to tools and click on internet options, go to the connections tab and click on Lan settings and uncheck all the boxes and restart Internet explorer and you should be able to use it as you would usually.