MSN Virus?

[cruciarius]

Occasionally I get logged out of my MSN and Adium tells me I logged on in another location. I just usually ignore it and tell Adium to reconnect. However, this time I was in the middle of chatting with someone on MSN. They told me that during the few seconds that happened, "I" messaged them saying this:

Hey check out the pics from the crazy party!! they are nuts LOL! go here to see (with a link here)

What's causing the "you've been signed in at another location" and that message, when I'm clearly not signed in?
How do I stop/fix it?

[Dimmuxx]

Change your password and don't use sites that claims to show you who blocked you or any other stupid stuff.

[cruciarius]

Alright, I changed my password yesterday. Haven't had it happen since.

For the record, I've never been to such sites that you described.

[Dimmuxx]

Okay, maybe you logged in on some infected computer or something then. Somebody probably had your old password for some reason at least.

[cruciarius]

I have logged into my messengers when I visit my brother, sometimes. However, he also has a Mac. I suppose it's possible that someone there went to one of the sites you described.