Need help with browser ads showing up

usual stuff like check browser extensions (all browsers, especially ie), run antivirus and check all startup processes and double check all again while in safe mode. Even simple stuff like Microsofts own security essentials, Ccleaner and spybot seemed effective at sorting my neighbors laptop out and stopped them bugging me with these issues.
Steam getting covered in ads is new one to me though. I'd probably keep eye on any suspicious activity on accounts after got this all sorted. Maybe even change passwords after all clear just in case.

Sometimes I think easier revert to day or so old (before this started) system restore point then start av scans.

Congratulations! You've now learned not to randomly install software on your computer. Always make sure to check for reviews and third party opinions on any software you install, including what will inevitably be recommended here. Next, create a new user on your computer without admin privileges and only use the admin user once you are absolutely certain about the software you want to install.

As for what you have now, it is a form of malware. I strongly recommend not visiting any sites relating to financial information, or inputting your credit card details until you are certain the malware has been fully removed.

To begin, there are a number of programs that will help clean your PC. Malware Bytes, Ad Aware, are highly recommended. Personally I find Hijack This to be wonderful solution, but you WILL fuck up your computer if you don't know what you're doing.

I had something similar a few weeks ago. However I have a shocking memory and can't remember exactly what I did to resolve it. All i did was google the problem (including the type of advert popup) and followed the instructions. Sorry this is incredibly vague but as I said, my memory is terrible.

Use, and learn to use AdBlock Plus and NoScript addons... Furthermore you can additionally use FlagFox addon, which shows the servers location. Oh, I forgot to mention, they are Firefox addons. (AdBlock Plus is available to Chrome, but do not forget to add at least 1 list)

malwarebytes.

Whats your antivirus? It should have stopped such downloads. It should have stopped you from going to the site in the first place. As you can tell I'm sure, your PC is infected. check out google for guides on cleaning your system. You will find some great sites/forums with instructions on how to do it with free programs.