I've never seen that issue, but I would say that McAfee is notoriously bad with its retail consumer offerings when it comes to virus/PC protection and messing up things on PCs. I gave up on McAfee two years ago and went to Kaspersky, which is a dream. Runs smaller, cleaner and virtually trouble free.
Are you using IE as your browser? Which version? Make sure you're using the latest (9.x). That's the one Microsoft keeps patched these days.
Also, are you keeping your Windows OS patched and up-to-date?
You may want to try installing Google Chrome as a separate browser and use your Google toolbar on that only. I don't use Yahoo or Bing - I don't care for Bing and have never needed Yahoo with Google toolbar on board. You shouldn't need to login to your Google account for the toolbar to work.
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