You should check your last installed programs for ad/maleware if you find something try to uninstall it,if it doesn not let you unisntall you should check your programm,programm data and programms(x86) folders for anything suspicious,if you are not sure what the programm is you should google it,in 99% of the cases this should clarify if it is a virus or not.
If it is just delete the suspicious folder and remove it from you trashcan.Better yet,if there is an unnstaller in the folder USE IT.You should check your these folder regularly.
Also you might want to check this if you use google chrome :
Go to Tools and then to expansions,remove all expansions you did not installed deliberately .