Three months back my HP Desktop Computer 'died' and, for the price of what mikey has paid for an AV programme, I bought a re-furbished Lenovo tower which is loaded with Windows7 and came with with Defender.
Having never had any problem with Microsoft Security Essentials which was loaded in the HP, it was my view that Defender was basically an up-dated version of MSE and there was Not any need to pay for an AV programme. Consequently, I am somewhat like Togo and am quite happy to trust my luck with Windows Defender; along with the free edition of Malwarebytes.
Hans.