Apparently someone hacked my account using that same site, a link that someone else sent to me prior, whom I'm guessing also got their account hacked. I'm not entirely sure how this hack works, so in the meantime, do not follow that geocities link.
For reference, this is the link in question:
http:// geocities.com / my_family_portrait /
I've added spaces so that the link is not clickable. I'm hoping someone with more experience than myself in these matters can figure out how this took place, so as to avoid the possibility of this causing harm in the future. I'm not even using Yahoo's official client, so that makes me even more curious just how this hack took place.
What does the hack do? I'm not so sure. I know it randomly sends IMs containing the link to other Yahoo accounts on your list, but it appears to do so at random. I've detected no viruses or the like, so it's further confounding.
As far as I know, my Yahoo IM account is now fine. I've changed my password, and I haven't seen a reoccurrence of this. If anyone else does get my account sending this geocities link, please let me know, and let others know if you get the link from them.