Well twice, actually. It only happens on my DS, and it happened in two different threads, so I'm assuming it's an ad.
Basically, a Java window opens saying something like "It is advised you get a personal anti-virus scanner". When I press cancel, it directs me to a site that looks like my computer, saying I have a virus.
I think the site was called Online Computer Scanning. It didn't affect me, seeing as though I doubt viruses affect DSes or other consoles, but if someone else is getting that on their computers then it's going to become a problem. :v

If that doesn't help, I could wildly browse DD on my DS, and check the address this time...

Yeah, I've been getting it too. There's already a thread about this.

It's just an ad with script to try and make you downlowd some crappy malware to get rid of the fake viruses it reports. I'd love to remove the add that its attached to but I don't have that power, all I can do is report it to the right guys and they're not at work until the weekend is over. T_T

Besides, we don't know which ad it's attached to.

If I had my way NO ad would be allowed to have javascript.