Help wanted with URL:Mal infection

Dear people,

Sinds 12/01/2015 after installing Rainlendar 2.12.2 I have a virus infection on my pc

info:
HP Pavilion
Windows 8.1 64-bit x64-processor

I use Explorer, Firefox, Torch and Chrome
when one of these browsers are open or windows explorer is open I get pup-ups from Avast Premier telling me that they blocked a site from openning with the mention that the infection is a URL:Mal

I did already a start-up scan with Avast
I did already a full scan with Microsoft malware removal tools
and I did a full scan with Hitman Pro

they all found and deleted some Trojans and infections but the pop-ups keep coming

is there something I can do to clean up this mess or do I have to completely format my pc and do a clean re-install?

is there someone who is willing to help me please?

warning: I know something about pc’s but still consider myself an amateur on these matters so please be specific and clear and have patience.

My native language is Dutch (Nederlands)

https://forum.avast.com/index.php?topic=53253.0