Istvan Gabor wrote:
Hello:
Please correct me if this is not correct. As I know GPL states if a program or part of a program or its source code licenced under GPL is used in another program the other program also has to be licenced under GPL and its source code have to be freed too.
Depends on how it's used, it's a complex issue. But normally yes, you're right
My question is how one can tell if a compiled binary uses GPL-ed source? Can't one take a GPL-ed source, build it in his program, compile and then sell it without telling that he used a GPL-ed source originally? How this could be prevented?
It has happened on a few occasions. Usually the developers look at the binary code, and if there are enough similarities between the two programs, they will notify the suspected infringers. As far as I know, it has worked so far. Another way is to see if bugs present in the GPL program is also present in the other one, or other very specific behaviour. This was how they discovered that Microsoft was using the BSD TCP/IP stack in Windows 2000 (which they recently finally admitted, after the world had known for about 5 years or so) It is a tricky subject, and there is no single, simple answer.