How to Remove Win 7 Antivirus Plus 2013?

Hi there,
I have a big problem and I need help. Yesterday as I sat on my pc a strange program called Win 7 Antivirus Plus 2013 appeared. It says it's an antivirus and shows up the following message:
"System hijack! System security threat was detected. Viruses and/or spyware may be damaging your system now. Prevent infection and data loss or stealing by running a free security scan."
I have not installed it and it shows up for a first time, so I don't know what to do. It looks suspicious for it's 2014 now and the program is out of date. Can it be a virus and how can I remove it?
Thanks in advance.