Thanks Igor.

Your post inspired me to find the file marked “chest” (ok, that was a little embarrasing that I didn’t think of it myself.) There was a file in there marked 000001, which was the right size to be the virus.

I deleted the file manually, figuring that the worst that would happen was that the original file would return and Avast could catch it.

The file never came back, but my swap file did return to its normal behavior. Apparently, the worm was somehow still active. I will pass this information on to support@avast so they can research it if they desire.