I have a user called "S-1-5-21-1761633107-36919189-275499408-1001" that I cannot seem to remove from security permissions. Not to sound like a novice, but what is this and how can I remove it. In my user accounts there is an ASP.NET account I never installed knowingly. Are they related and what is their function. The main reason for my concern is that I cannot download from the internet. Everything fails then disappears. And if I can trick the machine into downloading something I cannot access it due to permissions although I have full rights. The machine is on a workgroup network and I have checked for viral infections. Any thoughts?

P.S. I am using Firefox and Chrome. I have IE8 set to block everything except updates. Webpages work, just not downloadable content.