Lately, I've been receiving a lot of trouble calls from clients saying their computer has a pop up window saying the computer is infected with hundreds of viruses and that their computer is unprotected. First thing I tell them is that those messages are fake and intended to drive you to the point where you'll buy the software.  That particular "malware" is very persistent and will not let you do anything else on the computer.  There's also a strain of that malware that totally hijack's your web browser thus preventing you from going anywhere except for their website.  This s a real nuisance and ridding of it can be as simple as running a few tools, or a major pain in the butt.  When I get a computer infected with this type of malware, this is what I typically do.