Spending money on Security? Perish the thought!
Correct me if I'm wrong - Windows Security Centre consists of a basic firewall and not too brilliant at that. No Anti Virus program.
Defender - Just an antispyware program?
Download three excellent programs for free:
Anti Virus Avast click here
Firewall Zone Alarm click here
Anti Spyware - Malwarebytes click here
These should keep you safe, plus a modicum of common sense in your surfing habits of course.