It appeared just after a tech discussion with a Yahoo Security agent during which I allowed him access to the computer by remote (Team Viewer).
Did you initiate the discussion with Yahoo Security, or did they call you? If the latter, it's important to note that there's a scam going around right now where someone will call and offer you tech support for a "problem" in hopes that they will be given access to your computer. If that is the case, your computer should be considered compromised.
If, however, you initiated the call, it's probably just some aspect of TeamViewer. Try uninstalling it and see if that fixes things.
I have swept for Spyware with macscan.securemac.com and cleaned all of the files recommended.
Note that MacScan is absolute crap. In my opinion, they should be shut down for scamming people.
I recently did a test of 16 different Mac anti-virus programs. I tested them against 51 different Mac malware samples. MacScan only detected 2 of them. It missed a number of things that it claims to detect. See Mac anti-virus detection rates.
If you want to do a scan of your computer, you should use something better, like Sophos. However, it's important to note that if someone has been given remote access to your computer, it wouldn't require malware to make your computer compromised. There's a lot of perfectly legitimate software that could be used maliciously to give the hacker continued access, and that wouldn't be detected by most anti-virus software.
