Hey I've noticed this the second time now.
The first time it happened was yesterday.
Sometimes when I open a thread i get automatically redirected to updowntuv.com which, in broken german, asks me to download a JAVA update.
I am pretty sure that it's an ad somewhere on the site because it only happens on gamedev.net which is whitelisted in my adblocker.
Unfortunately I cannot tell which ad it is because it happens so quickly.
Do you have any say in which ads are being displayed?