Abuse of GPL or similar license

[Jimmey]

What is to stop someone from using GPL'd code in a closed source application, possibly for profit? I mean, wouldn't it be impossible to tell?

[Sporkman]

What is to stop someone from using GPL'd code in a closed source application, possibly for profit? I mean, wouldn't it be impossible to tell?

Well if it's large blocks of unmodified code, perhaps the compiled binaries would have detectable "signatures" that could be searched for...

But just the threat of massive legal liability would probably deter most companies from building GPL'd code into their closed-source apps. Cheaper just to re-write it (perhaps using the GPL code as a guide), IMO.

[az]

One resource is the software freedom law center.
http://www.softwarefreedom.org/

By and large, legal action taken against GPL infringement seek compliance instead of damages. Eben Moglen says on his website that he alone was able to handle all the FSF GPL infringement cases for ten years without any help. Since the license is pretty straightforward, the lawsuits were simple to handle.