actually, this is not related to vBulletin but to AIM itself... i would suggest you report that brute guy to the
http://www.aol.com/ official website... and yes, their navigation is a crap, complicated to have support...
it is related to AIM security protocol, i don't think it is just a problem of displaying AIM usernames on a site that would make the password retreivable... anyway, they are the ones who can handle that security breach...