Nowadays rogueware (also known as crimeware or fake security software) are growing at a shocking rate. They use bogus pop-up alerts or warnings that scare you into thinking your PC has been infected and needs to be fixed immediately.
These programs often install Trojans and other unnecessary things on your computer without your knowledge. Sadly, traditional antivirus programs often left undetected them.
So if you ever had installed such a suspicious application on your computer, I recommend you to scan your PC with Norton Power Eraser.
However, as it is a cloud based scanning, your computer must be connected to the live internet. Besides, you should verify the detected file before removing them.