Thanks nihil and others.

In a day or two I hope to try a few things in safe mode. Meanwhile, I'd like to stay with the idea of a targeted attack. Let's say I have an online enemy. How would this person attack my puter? How would I experience these attacks? There is no pattern to these Ad Aware shutdown windows: some days quite a few, others none at all. If it were a virus on my machine, wouldn't it manifest itself with regularity?

I'm wary of adding too much stuff to my 2005 HP pc. Once I loaded McAfee for which I should have had the capacity, and my system crashed--so no more McAfee. Most of my crashes are system 32 failures caused by a hanging download, i.e., the system failed to shut down properly and required a manual shut off, which caused a big crash. After the last crash I got a clean re-install of Windows. With automatic updates, I no longer see security downloads at shutdown, so no hanging downloads--big relief for me.

I still run Office 2000, which I much prefer to the bloated later editions.

Years ago, my pc at the time became so clogged with viruses in a short time that one morning I could not turn it on. I asked the techie who cleaned up the machine if that could have been a deliberate attack and he said, quite possibly. So I'm not paranoid that my machine might be currently under attack, albeit a weak one.

I run CCleaner before I pack it in for the night.

Thanks,