When you get your instant messenger from a 3rd party site, then you need to be sure that they have what you need. You also have to be sure that you will not be getting any nasty surprises along with the new software.
If you want to keep your system safe always evaluate a download site before you click on the link. Also, just to be on the safe side always use your virus scans when you install a new piece of software. It is better to catch a problem early if you can.