I registered just to say I ran across something similar on the US Degroot+ server tonight. Server loaded, I got to the MOTD, and my anti-virus promptly went berserk--I got 6 URL:Mal threats detected. When I loaded into the game my AV stopped popping up warnings, so I figure it has to have been connected to the MOTD/ad.
Now, it is Avast, which does have a history of false positives with URL:Mal threats, but I figure it's worth mentioning all the same. Especially as you guys seem to have switched ad servers recently. (I haven't played on Degroot+ in a few weeks, but when I was there last you were still using Pinion and I didn't have any difficulties.)
Managed to snag a couple of the warnings before they disappeared, so here's the relevant URLs:
i.imgur.com/AwHggeW.png
i.imgur.com/ev9lgdR.jpg
As far as I can tell it didn't attempt to download anything or do anything with Java on my PC...possibly because it was immediately blocked by my AV. Hope it helps.