I've also experienced this issue. I'm quite sure that it's from a rouge ad that is rotated on this site. The reason being that I had it happen on the home page so it's not from a rouge user posting something.
Also, in my case with the current Chrome Beta it's not just a single window, it's a full on redirect. *shudders*
Looks like this is coming from China.
If this pops again I'm going to have to blacklist OCN with Adblock+ again until this is fixed.
I get the same redirect. Just exit the windows and whatever you do don't click OK! It is a major pain in the ass because it pops up every 10 minutes on the website. I use Chrome and have had it pop up on 4 different PC's.