I was away from my computer for maybe 5 minutes. When I came back to it, the "This was a free session hosted by TeamViewer" popup was on the screen. My web browser was open to the Paypal login page, with my account name in the user name field, with an attempt to purchase a $200 Ebay virtual gift card.
Needless to say, I immediately exited TeamViewer and disabled its Windows auto-start. I also immediately changed my TV, Ebay, and Paypal passwords.
But there's a bigger problem. If this program isn't secure, it immediately loses all usefulness. The whole point is to leave teamviewer running on a computer that you're not at, to be able to establish remote connections to that computer.
If, by leaving the program running, I am giving *someone else* the ability to do the same thing, then there is no way in HELL that I am going to continue to trust this program.
And I now know that that's possible, since I watched it happen. If not for the fact that my Ebay was logged into my work account, and my Paypal was logged into my personal account, I would have been screwed for who knows how much money.