Borrow a trusted friends Mac and go to a reputable AV source ClamXav and Sophos (for Mac) come to mind. Download to a thumb drive (pen drive) and then virus check it. Then copy it to an easily discovered place on the mac hdd like downloads or desktop and make a bootable usb drive and install the AV scanner/removal tool. Shut down you infected mac. Insert the usb (trogan) removal tool and hold down the option key. Continue to hold as the mac boots and select the usb drive as boot shows options. Trojans usually load as the EFI calls the OS, so not running the OS provides the most effective removal. Also many malware are self seeding and somewhat immune to AV scanners in the OS.