Screen Share risks - malware? key logger?

Hi -

I accidentally called what I thought was Apple Care yesterday but it was an "outside" provider. I did agree to share my screen with them and they had screen sharing privileges for about 10 minutes. I never typed in my password or knowingly downloaded anything. Obviously, once they said there would be a charge to fix my "problem", I realized they weren't Apple and disconnected immediately.

Can they have installed a key logger or any other malware without my password? And if so, how do I locate it??

I have checked LaunchAgents, LaunchDaemons and the settings to see what automatically logs in when I log in. There appears to be nothing wrong.

The computer is brand new and I called them while I was doing a full backup, so the option to erase and re-install from TM isn't really an option unless I take off all my files to another HD and then start over.

When I called Apple they said not to worry, but I am still worried.

Thanks!