Can affiliate commissions be hacked & stolen?

You have not provided enough details for anyone to be able to give a proper answer.

What was the product you were promoting? How were you getting traffic? Did the traffic die down or the traffic was still being sent to the affiliate offer and the sales didnt happen?

If you were tracking the traffic you were sending to the affiliate offer, you could contact the program owners and ask the reason why sales were not happening even though the traffic is still being sent as before and you could show them proof of the traffic. If you did not receive any satisfactory reply from them, you could direct your traffic to another related affiliate product to see how you fare.

But if the traffic itself that you were receiving died down then that is a different issue. In that case you have to look into the reasons why you are not getting traffic as before. You need to analyze whether you were getting all traffic from Google and the rankings went down or what else happened?

I have not heard of stealing affiliate commissions on a big scale as you are suggesting. However, using a raw affiliate link can be recognized by some buyers that may belong to the same network and substitute their affiliate in place of yours.

That is why masking your affiliate links not only to protect them from other people stealing your commissions but to make it easier to track and make the link look much nicer.

Best regards,
Steve Yakim

This is actually common.

Here is a good thread about it. It is called affiliate link hijacking

There are many different ways it can happen, so I am not sure which one may be happening to you.

Yes, it is common, I believe this kind of problem can be occurred. About 5 years ago, I faced similar this problem.

It is possible. A few years ago Clickbank had this problem. That is why they changed the encoding of links.

Well, of course it can. Almost anything can be hacked/stolen on the Internet.

I'm with anwar001 in that you should check your traffic. If it hasn't changed someone is playing on you.

Read the article from the thread that JosephC linked, it'll give you some ideas.

It's very easy of a rogue plugin has access to your site all it has to do is replace your link.

It's easy check by clicking on your links and see is it your link.

Or your problem could be down to Google changing the goal posts again.