is possible that 'it' has not been eradicated completely.
absent however any additional information like the name of the file/ software, whatever, in question and what your O/S is, it is impossible to give you some methodology to clean 'it'.
Recently (3 days ago)my computer became infected with a file that is an add on to IE. It installs itself, and then runs a program called something like dee.blah.gg (Im not entirely sure). This installs a new toolbar, adds loads of stuff to my favourites, and puts icons for online casinos on my desktop. Oh, and pop ups appear even when Im not using IE (Im on broadband though).
Now, the first time it came, I simply tracked it down (not hard, the folder isnt even hidden) and deleted it. Job done I thought. The next day it was back! Same process didn't work, so i ran Adware SE, McAfee and Hijack This. Combined efforts tracked it down (it resisted deletion and hid itself), isolated it (was quite attched to IE me thinks) and deleted it. Or so I thought. I also now run Firefox 1.0 instead of IE (how did I survive without tabbed browsing?).
Anyway, using it todays, a pop up appears! The program isnt even there anymore! Anyone got any idea whats happening here? Admiteddly, it was only one, but I was surfing a site Ive been usign regularly for 6 months, and never a pop up before. Any advice on a cure and some decent prevention (Windows XP firewall sucks, and it waltzed past McAfee) would be good! Cheers, nicebutdim.