Usually 'strings' on the binary shows up tell-tale signs. Granted that means the 'smart' infringers are likely to slip through the sieve, but at that point the

Usually 'strings' on the binary shows up tell-tale signs. Granted that means the 'smart' infringers are likely to slip through the sieve, but at that point they'll have to essentially be re-writing the code anyway, and lose most of the benefit that they'd get stealing the GPL code (they'd have to hand-roll any bug or security fixes back into their stolen-but-obscured GPL code)