I don’t think this problem/solution is much different in older versions.
Problem: when you send a link from Communicator client to another, the link isn’t clickable, has a _ (underbar) in front of it, or both. Results may be different on different computers. It’ll look like this
Solution: Two things are happening here that are not related. The first is the OCS Server (and Edge Server) have the URL Filter enabled, which are adding the _ underbar to all links. Also called “Intelligent IM Filter”. You need to tone that filter down or disable all together to your liking. If users are coming in through an Edge Server, they will follow the Filter settings of the Edge Server they are using, which seams to supersede the Front End Server (my guess is the most restrictive wins). So be sure to set it on both servers separately. Results were instant in new IM’s.
The other issue is the lack of a clickable hyperlink. If you disable the URL Filters above, the underbar goes away but links are still not blue and underlined. To fix this you need to apply a GPO or set a local registry setting to allow Communicator to make hyperlinks clickable:
new DWORD EnableURL=1
After that exit and restart Communicator.
In both of these cases they are secure by default, which is great; but even years after this features release over several versions their use and configuration are still a mystery to most starting out.