Shoutbox

Messenger Plus contains an optional sponsor program, that you chose to install at this screen;

That isn't a virus just a small few adverts. Some of the lesser quality antivirus products can say that Messenger Plus is a virus, however it is not. If you have installed the sponsor program that can be removed, easily, and you can still use Messenger Plus.
Detailed instructions on how to uninstall the optional adverts can be found in this thread.