A few years ago, I tried using Yahoo chat, but there were too many bots and I kept getting too much spam in my Yahoo mail from them. I had to block a lot of users, including one that sent an add request without a note that turned out to be an ex who I had lost touch with, because his userID/email looked like the usual spammy bot name.
Later, he emailed me from his work months after I had tried and failed to get back in touch w/him, and he wanted me to write back. I asked for a personal email address, since that would be more appropriate. He then gave some lame excuse that his home PC had viruses (normal people take care of viruses instead of just leaving them on their computers!)
Well, then he gave me the address anyway, and it looked familiar, and sure enough, I saw it in my blocked list. Soon after I unblocked it, hit him up to add me, then he accepted, I got shitloads of spam in my inbox and had to not only block him, but delete the account. I tried again later, and same shit. Trouble is, how do I prove it? And how does someone spam someone else like that?
The year after that, I looked him up online and it showed some other Yahoo email addresses for his name, but I forgot where I found it.
Recently, I looked those addresses up and they showed my IP address! My old closed Yahoo addresses showed my IP address too. I have good antivirus SF, I guess what I need is to understand proxy servers. Any advice or similar experiences?

Some friends and I were hit with spam involving acai berry. We tracked down a temporary solution being to change passwords. Proxy servers are a good idea too.