My ex-wife had her computer really hosed. We are really good friends still and I am still her goto tech support. It turned out that she had been running with no anti-virus software for 4 months. Her computer STOPPED me flat from installing it again.
I normally handle this easily by popping out the drive and putting it in a USB enclosure, mounting it as an external drive and running a full scan. It cleared like 60 viruses off the drive.
I popped it back into her computer, fired it up, installed new antivirus software. and then I made the mistake. Put it on my network to download new virus definitions. In the 5 mins that took, the malware hopped to the next machine on the network.
I am not going to mention the name of this virus. Because if you Google it one of the top ten hits will infect you with it.
--What did I miss?