Avast is one of the three main contenders in the free antivirus world, AVG and Avira being the other two. As with those two, there are paid-for products in Avast’s range with more features, but the free version has several useful features of its own. 
It starts with the antivirus, anti-spyware and browser protection combination, but also includes a home network scan and Dropbox for online storage. The network scan looks at your network settings and passwords and reports if any of them could be more securely set or stronger.