Yeah, Those are quite common, They aren't always viral though, Although your example sounds like it is.

Sometimes, services like ebuddy and other online messengers in their small print state that you are giving them permission to access your account for the purposes of spreading the word of their service. So they'll access your account, Post ads to your contacts and leave.

Your contacts are left puzzled because usually they'll know it doesn't seem right from you...

Sometimes, and in your case though, they are viral, The point of any virus is to become as wide spread as possible and cause as much damage as they can. That's why black hat hackers write them.

They can be really difficult to remove, Making sure you have AVG Anti-Virus installed is a good way to go though, as that usually detects viruses as they try to execute.
There is a program which is specifically designed to remove the MSN Viruses but it doesn't remove them all. It's worth a go though for the tiny file size...
Download MSN Virus Cleaner

Generally I'd avoid online messengers unless absolutely necessary, When you do, Read all Terms & conditions before entering your username & password, After all you don't know what your giving them permission to do with those details...

 

omg that is exactly what i've got too,i get messages like that all the time, and people ask me why i've sent them things i've never sent all the time
i'll try that cleaner see if that helps.  

it's scanning now i think. i'll see what happens