I'm not that familiar with Windows 8 or 8.1 but the built in security (Microsoft's own) seems to be OK. So, MSE and/or Defender should do the trick.
However, in my own tests with free AV software on older MS OSes, Avast did better than MSE and AVG when I tried to deliberately infect a computer with the MET Police scam. As Avast is free it may be worth considering if you're not happy with MS's own offerings. Hope that helps
