Well, I am a little more 'puter savvy than I am chainsaw savvy, but not by much, so I'll throw in my two cents...
This site was/is compromised. Most likely targeted due to the fact that it has a relatively high user base and visitors. You see, the redirect will (potentially) make money from every user that tries to access this site, and happens to click on the crap ad link... That's how site ads work... Typically the payout is a set amount per user hit. It's not very much, a few cents maybe per hit, but with thousands of users on a daily basis it could add up...
That being said, your personal info is most likely not compromised, since the hackers don't care about your log in name, nor your password. They don't care about your advice given concerning chainsaws. In fact, even if they logged your username and password, the most they could do is log into your account here, which typically contains nothing of value... I mean, you don't have your Visa number and expiry date as your sig, right?
It's always a good idea to run an up-to-date antivirus program on your 'puter, which should signal to you if something funky is trying to enter your system that shouldn't be. It may even just auto-block it, or a port, so you wouldn't even know.
Coles notes? Your accounts are fine, the hackers don't care about you nor your account, the Administrators of this forum are probably pulling out their hair trying to fix the issue, and when all is said and done they'll wished they hired a pro to set up initial network security, and to possibly maintain it also...