They've got some automatic filters in place. If you include a suspicious keyword in a link, your message will fail to send. I can understand why they're trying to protect their users against malware and all that, but this is an annoyance that I could do without.

This led to the rather stupid situation where I was at work and couldn't even send a link pointing to our company's website. In that case, the word "download" in the URL seemed to be the culprit. If I have to make a guess, Imageshack might be getting blocked since it contains the word "hack" in it's name.

Actually, Imageshack is blocked at a lot of places - there is good reason, considering all the 4 - 5 annoying pop-up windows it now gets (if you use it with internet explorer), but unfortunately some of use are simply used to the URL and still use it, and therefore should not really be blocked...

Of course NOTHING should be blocked by an instant message program (content wise) - that's fucked up.