We do have a few repeat customers yes, usually because there machine wasn't secure enough, though.
Some info on SideStep Here. If you don't use it go ahead and fix it with Hijackthis.
O16 - DPF: {640B39C1-D713-464F-92C3-75BD972B95EE} - http://download.side...00720/sb028.cab
Also, see if you can delete C:\WINDOWS\sahagent-fellymedia1002.exe from normal mode, otherwise go ahead and boot to safe mode and remove it.
My advice for trying to keep malware off in the first place though would begin with some bare minimum protection, though.
Are you still having any pop-ups/redirections?