I had the same problem. Been searching forever for a solution. Apparently I found one and miraculously it worked. Refer to the link below for more info. Hope it helps.
So I've had quite a few problems with my computer recently, it started when random ads would pop up using iexplorer, even though I always use firefox and never had iexplorer opened, when this was going on, iexplorer.exe would still run in my task manager even though I had closed all the windows, and would be running in the background on startup. Then my computer starting freezing a lot, not restarting, not starting at all...etc
I also found 3 foreign .exe files in my task manager, one of which was prunnet.exe (can't remember the other 2) and found them in C:/WINDOWS/system32 and deleted all three, this seemed to stop the freezing but the pop ups still happened (along with random sound clips), I then found 'RON ads by agadoo' in my control panel and uninstalled that which stopped the ads.
This was all in the last week and ever since then my internet is extremely slow, and whenever I do a search on google or yahoo, when I click on a normal result link I always get redirected to random pages (and this happens for any link result, i could search for google and click on the link for google.com and end up on some church site...), this doesn't happen if I copy paste the URL from the search results and just go to the site. (Also if I do a search after just restarting my computer I can get to the correct page, but after a minute or two the redirecting starts)
One more thing is that ever since this started my spybot S&D will not run, if I click on it, it runs in my tast manager but does nothing, and Mcafee can't find anything else wrong.
I know this is a lot but if anyone has any ideas on how to fix my problems that would be greatly appreciated!!!