It proved to be deeply entrenched and intractable; I'm doing a full system recovery. Will that get rid of it? Maybe. Still can't figure how I got it in the first place.
Saved some text files on a thumb drive. If I can figure out how to be sure they're clean -- pipe 'em through a Mac and back out on a fresh USB drive? -- I won't have to start over on the current chapter of "Dropping In" (which was supposed to be posted already!).
Update: Recovery recovered and I have Malwarebytes and Spybot - Search and Destroy loaded, along with AVG. Plus I put Q10 back on it. It just shut down and powered back up okay. Fingers crossed!
Introduction to Sim
2 months ago