Hi! A friend of mine has been using my iMac for some days. I think that he could have infected the system with some trojan or virus. I know that he had downloaded Adobe Flash from a suspicius site. I also had and external hard disk connected to it so it could have been affected to. if hard disk is infected and I format the iMac and then connect the hard disk to the iMac, can be the iMac affected again? What can I do to be 100% sure that it is clean? Clamxav show it's OK, but I want to be sure. And finally, any advices about security in Mac OS, specially about user accounts?