I encountered this annoying web site redirect when I was using one of those YouTube downloading sites. Got stuck on it. Force closing the browser didn't help. I tried blocking it with AdBlock, but didn't help. Luckily I was using a 3rd party browser. So just removed and reinstalled the browser. So that's not necessarily good news for anyone that has this issue with browser in Cydia or if this happens in Safari.
But one thing I didnt try, go in airplane mode and see if you can close that stupid site this way.
Edit. Ah, see there was way to fix it as I was typing up my post.