It's just Messenger spam. This type of popups make use of Messenger Service in Windows.
This Messenger Service is NOT in any way related to Windows/MSN Messenger or any other messenger tools.
You can safely disable the Messenger Service. Go to Start > Run and type
services.msc and press Enter key. In the Services window, navigate to "Messenger Service" and right-click it, and select "Properties". In the Property window, click Stop in the "Service Status" option box. After this, in the "Startup" option box, select Disabled from the dropdown menu. Click "Apply" and then "OK".
There's also a small tool called
Shoot The Messenger, using which Messenger Service can be easily disabled.