I'm 100% behind Hans's answer but I'll just mention one thing:
The Premium (i.e. 'paid-for') version of Malwarebytes Anti-Malware is, like AVG, software that continuously 'runs in the background', watching out for any nasties that might be heading your way. (Like Hans, I don't think that you actually need that version).
However the free version of the program is only 'run on demand'. That means that it will do absolutely nothing unless you remember to actually run it occasionally! I suggest running a scan with it about once per fortnight or immediately if
(a) you've started seeing odd things happen on your computer (such as lots of pop-up ads appearing) ; or
(b) you realise that you've clicked on something (such as an email attachment) that you probably shouldn't have done.