I waw browsing online earlier.. and suddenly an error message for 'SysFader.exe' popped up, saying that Internet Explorer had attempted to read memory at an invalid address. It looked like a virus, and stayed on my screen even though I hit Ctrl-Alt-Delete. I figured it could be bad.
Then, I went on the desktop and looked it up. Turns out, sysfader.exe is a process that smooths out transitions between applications on systems running with Nvidia graphics cards. It's not a neccessary process, but certainly isn't a virus. I hit cancel, and it turns out all that happened was IE closed the malfunctioning tab. A virus scan turned up nothing except the usual rogue's gallery of harmless tracking cookies.
All seems to be functioning again, but it was scary for a few minutes.