How to block fake servers like Fastpath

Synopsis

Automatically blocking the servers in the Windows Firewall (How to block fake servers like Fastpath)
How does the spam work and why should you block this?
If you are playing a source engine game infected by these fake servers you will see a number of different servers spam your list that will make you end up on a different server than you thought you would join.
At the moment of writing the Fastpath community is the primary abuser with this method.
When you joined one of these servers you can still join other servers, but because of the large amount of servers they spam and the fact they can use players joining the servers to fake having a high player amount for a long time it is easy to get trapped back in.
One of the most important reasons to block these servers outright is that by joining them they can use your steam information to fuel their spamming method.
They capture your steam details including the unique authentication you used to join the server, and instead of removing this like other servers do when you leave they will instead put your information and nickname on all the other fake servers for as long as your information is valid.
Causing these servers to appear very high up the server list making it hard to avoid them for others because they can spam as many as they want.
On top of this they will fake any information they can, different map names, server names, server names of popular servers you like, player numbers and even ping (Although they fake the ping in game not on the server list).
And during the times less HL2DM players are online their effect is amplified since it will be harder for steam's server to detect which server has legitimate players online.
Because they constantly change their details and the ports the servers run on blocking them using the in game blocking buttons is almost impossible.
This method you can use to block the spam properly.