Some malware does do that kind of thing.
If you don't already have them, download and install the free versions of Malwarebytes from
http://tinyurl.com/d5jtuz and Superantispyware from
http://www.superantispyware.com/ (there is a link on the page to download the free version). Reboot your computer in safe mode with networking, then run each program in turn, making sure you get the latest updates before doing a scan. Delete anything the programs find, reboot and hopefully the problem will have been fixed.