Even though AVG denies their being associated with their software, they could
be AVG log files. If you use AVG's scanner this could
be the source. See this thread here...
You might try the software mentioned in the last posting on page 1 of that thread and see what's locking the files.
The final post in the thread continues to deny AVG association and gives a plausible reason for the results in the posting before it. If you don't use AVG then that would seem to justify their claim even though the text is found in their DLL files according to one poster in the thread.
This is the only thing I've been able to find although my original thought was that it might
be some sort of Torrent log file since you indicate it contains sites and searches you did not make. I continue to harbor that suspicion; do you use a Torrent client and have it running in the background all the time?