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OK, I have only heard this as a rumor, but it was from a very reliable source. He claimed he shut down one of his customers websites who refused to pay him, WITHOUT putting any code on their hosting account or wordpress theme. He said he didn't play games and since they refused to pay him the $30K they owed him, he took drastic measures.

Does anyone know how to do this? I am in the same boat (although not nearly as much money. He is just being a jerk). I promise that I am not wanting to use this on anyone in an unethical manner as I am not that kind of person. I just need to find a way to force him to pay what he owes me as he is making money off what I have done for him and he is refusing to pay.

The next question I have is, if you know a way to do this, is there a way to prevent it from happening to me in case someone tried to use it on me?

As my first post on the BBHF, I hope I am not overstepping my bounds with such a question. If I am, please forgive me and I will gladly remove this post.

Thanks in advance for your answers.

Imho this is a matter of skills of your customer - or the jerk. I can only consider a method with additional code on the website.
For the most simple way on future projects you should consider a simple request to a file on YOUR server. If this request returns a false, you "exclude" the whole page - but remember to implement a fallback, in case your server is offline.

In a no-expert-way this should look something like this
"if>FileExists>(if>FileCheck=TRUE>LoadPage>Else>Error)>Else>LoadPage"
How you implement this is up to you. I hope this served as food for your thoughts.

I can not imagine a way without a coded backdoor - Also I wouln't tell you, if I did it like this.

Cheers!

It's certainly possible, but there is most likely NO LEGAL WAY TO DO THIS.
Unauthorized messing with other people's websites, servers, networks or whatever is outlawed in most civilized countries.
A possible loophole could be, if you put in the license agreement that whoever installs your scripts/software on their server agree that the software may block the website working when used without valid license.

Advice?
Use Cloudflare.com for protection against hackers and such.
And don't use software or scripts which you don't trust on your server/hosting.

If you have trouble with a customer who won't pay:
There are legal ways to make someone pay what they owe you. In the internet marketing business that might be more difficult, if your customer is somewhere in India, Suriname, Nigeria, Malaysia or wherever. So I would suggest insisting on pre-payment the next time.