I have 2 Gigabyte H97n-wifi boards and 2 Intel Pentium G3258 processors. Dont know the bios revision and these boot up but wont post.  So last night I was searching forums to see if others had problems.  Was wondering if these have the original bios which doesnt support the g3258.
  After reading through the forum my browser closed. I restarted and it closed again.   I ran malwarebytes and it showed all these pups etc.   I looked in Program files (x86) and there was coup mania, white offers, something keeper etc. About 9 all in total.   All had date and time of when I was browsing the forum.   I had adblocker installed and that had silently been removed as well.  After cleaning out, I started firefox and it had browser redirect to adult sex site.  Cleaned all that up and Windows defender, Spybot ( i downloaded to double check) Malware bytes all showed system clean. I ran online Housecall and it shows clean.

I run Windows 8.1 64 bit with all updates and have MalwareBytes and just built in Windows Defender and in Firefox adblocker (which I know site managers hate) to try and prevent this happening.

So do I need a paid version of an antimalware/ antivirus to pick these intrusions up as happening since neither Windows Defender nor free version of Malwarebytes prevented this happening.