You can block the vast majority of "bad" sites (and many add sites) by modifying the hosts file on your PC. A host file exists on most every OS I know of and is a hold over of the old days of manually updating Domain Name Service (DNS) records. Sadly I remember having to do this on some *Nix systems back in the day.
Background: Each time you or your browser makes a call to a website, a DNS query is executed locally against a file called hosts on your system and if no answer is found there, the query is sent out of your box to an Internet based DNS server. This happens in the foreground (you enter in "www.stromtrooper.com" and hit enter) or in the background when the page you are calling, makes a call to another page so that an ad can be served up.
This process can add latency to your page loads due to network congestion, inaccurate information in the DNS system (it is now a shared database which is distributed throughout many servers on the Internet and updated automatically when a change is entered at some authoritative point) and a for slew of other reasons.
The order of DNS look up is the local host file, then the Internet DNS system (there is some caching in there as well, but I"m not going into that detail).
So to block unwanted hosts from displaying or being reached (this was an early form of parental controls in my house) you would add an entry to your host file that looks like this:
or I believe today you can also use:
So when your web browser makes a DNS call to your OS, the OS looks at the local host file, sees the entry for ad.crwdcntrl.net as 127.0.0.1 (or 0.0.0.0) it thinks it has an authoritative answer, does the whole HTTP get process (now sending the request to YOUR local PC, not the server on the Internet) and gets nothing back and you end up with a HTTP:404 error (page not found) where the add should have been.
So to make life easier, there are smart people out there who've decided they will maintain a community compiled hosts file that one can use to put on their system and block many of the ad and nefarious sites that cause us so much trouble.
The most popular and one I have used in the past is Blocking Unwanted Connections with a Hosts File
There are others, just do some Googling to find out more.
If you a running a *Nix based system, you will be looking at the /etc/hosts file.
As a test, I just did this following the directions on the site on my PC running Win8.1 and had no hiccups.
This is what it looks like when an add is blocked:
- Be sure to make a copy of your current hosts file in case things go south on you, but the site above has a simple batch file that you run to do all this for you and it makes a backup copy of your original hosts file named hosts.mvp.