Today I verified that Norton Live Update is filling up my C drive. A couple of weeks ago, clicking on "Fix Now" did not discontinue the "Attention Required" message. About the same time, virus def's stopped updating automatically, and I started getting "low disk space" messages. After attempting to investigate the problem in my spare time, I began to suspect Norton as the culprit. I have been a loyal Norton user for almost 20 years and I did not want to admit the obvious.
Today, I cleared off almost 2 gig of space on my C drive. I then ran auto-update and, after it was done, I only had 613 MB of free space on my C drive.
Norton is definitely the problem.
Fred.