This exploit that no longer works, was originaly found for unix platforms. It was possible from the *nix platform, to send a Comment Crash (a string of '< !--'s) that crashed Windows AIM. The reason it was hard to exploit Comment Crash from a Windows Client to a windows client, was because when pasting a large string of comments into an IM, the executor of the crashes AIM, would die before the IM could be sent. It wasn't very long before Robbie Saunders (Creator of AIM Filter) found that by sending the string from his Local Proxy he could avoid AIM crashing on his side, because the Comment Crash didnt go through his AIM Client. There are other ways one could have done a comment crash, like using VB to simply type, '< !--' over and over again, into the IM-Box, and have it send. This would crash both the sender and the recivers AIM, BUT atleast they got crashed too. Another way to exploit comment crash was to use AIM Express, you could paste a Comment Crash into AIM Express because it uses the TIC/TOC Protocol as opposed to the OSCAR Protocol, and does not express comments the way OSCAR does on the client side. Actuly it is not really the protocol that allowed Express to exploit the comment crash it was the fact that Express is coded in Java. It does not represent comments in the same way that an Oscar based client does. (another variation of AIM Express is dSp AIM)
Windows based clients, do not show comments unless you hit 'F2' which allows you to view them. You cannot simply type < !-- into an IM (without the space between < and !) because that will be sent as it looks, because of the way the client handles it. You must copy and paste what you want sent from something like notepad, into your IM box.