However: I ran malwarebytes this afternoon, which found six trojans, none of them the one that AVG was reporting, and eliminated them
In my experience there does not seem to be a single AV program which will catch every piece of malicious or irritating unwanted software. AVG Free used to be very good but like most AV programs I have found it became clunky and intrusive with successive updates.
I now use Avast! Free which I believe is as good as any, does not slow the machine and is, of course, free.