trojan clampi- is it possible an i-Mac running Mountain Lion 10.8.4, could it have this trojan?

Very unlikley. Keeping your system software update to date is the best way to prevent malware.

Open System Preferences > Software Update

Select: Automatically check for updates

If that area is grayed out, click the lock icon to proceed. You may be prompted for your admin password.

No. From Wikipedia:

Clampi is a man-in-the-browsertrojan that steals financial information from companies that are sent to hackers to use for fraud scams. The virus has been around since 2007 and only affects Microsoft computers