of all the replies I didn't see the most important one:
(before replying, make sure you give proper and full explainations! Replying isn't a race!!!)
Plus! doesn't not include any virus what-so-ever!
Just make sure you download it from an official source:
http://www.msgplus.net
(or in case of the current special mess.be build, from
http://www.mess.be)
---
to further answer your specific question:
If it is a anti-spyware/adware tool that is giving the warning, then know that there is a massive huge difference between a virus, a spyware and adware! All three things are not the same by far!
Messenger Plus! includes an
optional sponsor program which is a small piece of adware (it is not spyware, neither is it a trojan, nor virus). This can be choosen to be installed or not; it is NOT installed without you explicitly saying so.
Some anti-spyware/adware tools wrongly flag Messenger Plus! as malicious (eg: Microsoft AntiSpyware). These warnings give you serious misinformation and it is only the setup of Messenger Plus! (thus not Messenger Plus! itself) which contains a way to install an optional adware; but as said, this is only when you explicitly told it to.
Such warnings can safely be ignored as there is no harm at all for starting up the installer, or Plus! itself. Just carefully read and understand the installation instructions.