mobile broadband: sth using my internet

[finrodfeleg]

I have orange mobile broadband, which tells you how much kb you are downloading. I noticed that when i was not using safari info was being downloaded, even when i quit safari, itunes and email. I did anti virus check with clam xav and found a trojan on my usb stick, which i then put in trash, only to find it did not delete. I also ran anti spyware and deleted some tracing cookies, which also got rid of the virus in my trash. I deleted all my deleted emails, emptied my trash, deleted my cookies. I then found my sharing settings were on so i turned on firewall (which was off) and turned off file sharing. Strangely something is still accessing my internet, but apparently i have no spyware or virus on my computer. I looked at my activity monitor but the only things running are root user or hp io class/mdimport, which i have realised are not ness a problem from these forums. Has anyone had a similar problem? Do i have anything to worry about do you think? P.S. what is the best way to learn about apple macs from a dummy level? Thanks :>