I hope they correct this before a final release.
I installed the sponsor and nothing bad happened. My computer didn't explode, I didn't get a virus, and it's all working perfectly well.
I agree with almost everyone here, when users see a notice from their antivirus about a software, they instantly want to get rid of it, and they stop trusting that software.
And knowing Microsoft, they'll do almost anything to get people to have their "awsome" antivirus program, which could mean lots of users getting the false notice about Messenger Plus!
/ 
