Ugh, there definitely is a problem with roundcubeforum.net. It's been infected/hacked. You can even see this when you use FF/OSX but it probably doesnt do much then. Firebug shows that roundcubeforum.net wants to get/run the following URL:
http://directmarketing12straight.in/in.cgi?walter
Quick google shows thats a marker for an infected site. It may currently be spreading somehow through IE, dont know if it can do something to IE clients.
This is not good for the reputation of roundcube. Anyone in contact with the admin?
Cor