Some years ago i made a nice plug and play script and released it to the web. Today i've searched for sites linking back to the product's page and i can count them with the fingers of my hand. Then i searched for a specific sentence part of the system and i find thousands of results...conclusion nobody is linking back despite i specify that the software is free and link back is required. How can i force those thousands of sites to link back?
You would need to email each site individually, informing them that they have violated your terms and that they need to put the link back or remove the program. You should also inform them that if they do not resolve the issue by doing one of those two things within 10 business days, that you will be contacting their web host.
You people are very nice. Giving 10 business days. As they have violated the license under which they have got the softare, you can take legal action without notifying them. Granted, court is never the ideal decision. The amount of time to give is personal preference, but I personally only give 48-72 hours, depending on the type of site. But, you can't force them. All you can do is start sending out emails and hope they listen to you. If not, email the host and let them know what is goin on. If that doesn't work, there really is only suing them, so if you feel like it would be a good return on investment to do it, then that would be ok. You could always take one to court, get the verdict, and if its in favor of you, attach a summary of it with your emails.
Clades that is pretty sad. I always assumed a certain % removed the links without permission. But I never dreamed it would top 50%. You make it sound more like 95%. The advice given above is about all I think you can do. Good luck.
You should start by contacting site owners and asking nicely why they decided to remove the link. Try not to use any sort of threatening tone or suggest that anything will happen if they don't link back. Sometimes people assume software was written by an evil money grubbing corporation, and will change their mind about leaving the link in there if they see a normal human being just like them wrote it.
Thats also true joebert, a lot of people would change their minds knowing it was written by a regular joe.