Let's face it, running a Windows PC is a bit like walking a tightrope when it comes to being online. There are just so many exploits and bugs that people take advantage of to get crap onto your computer.

Microsoft has started to take a bit of responsibility for their users' security and have finally released the Microsoft Security Essentials package.

If you don't have an Anti-Virus/Malware package, you should get this. If you're using a solution like AVG or Avast then you should consider this as well.

I'm using it on my machine now and it's great.

Microsoft Security Essentials