Incorrect display names - website addresses showing

Hi,
I noticed last night that a friends display name showed a website address
and had a comment saying see who has blocked you or deleted you from MSN -
something along those lines. She popped up online then went offline and this
happened about 3 times. Each time, there were 4 pop up boxes in the
right-hand corner of my screen, each one saying she had logged in, but each
with a different name. After about 10 minutes it displayed her normal screen
name and I thought nothing more of it. Then this morning, I added a friend
of mine as a new contact and her display name came up as:
www.EstasNoAdmitido.com <--Fijate quien te elimino y quien te desadmitio en
el MSN, again like the night before saying see who has deleted you, etc...
So I sent her a message saying "strange screen name" and she replied saying
it just says "Tali" (which is her name). I checked with a mutual friend of
ours and he also said she is just displayed as Tali. They are both using
Macs and I'm on a PC, if this is of any importance. I removed her and added
her again and it still displays the same screen name, which incidentally goes
to some sort of pornographic site...
Please can someone help me solve this? My AVG says that I have no viruses,
but it is only the free version...
Thanks,