Adware:Adware (or spyware) is a small program that is designed to show advertisements (in various form and degrees of intrusiveness) on your computer. It often reports personal information back to its owners. As a result your sense of privacy can be violated.
Gratisware is a malicious adware spyware that regularly shows unexpected pop-up advertisements. The threat tracks user Internet activity, records addresses of visited web sites and silently transfers gathered data to remote servers. It has the ability to update itself via the Internet. Gratisware can be installed by some ad-supported software. The spyware remains active while the user surfs the web using Internet Explorer.
Technical details (How to remove Gratisware(pop up))