Your GPL example detracts from the question: see this recent answer. Setting aside GPL-specific conditions, the legal underpinning of software licensing is copyright law, whereby copying source code or an executable is only allowed with the permission of the copyright holder. There are two partial exceptions: "fair use" (generally not relevant to software), and a specific statutory permission to copy software in particular ways (making a backup, plus the act of executing software which requires copying from disk to memory). The latter permission only applies if you have legally acquired a copy of the software.
Which explains why nobody sells copies of software, they sell a license to use software (a subtle, legalistic distinction, which is essential to modern software qua business). The terms of the license say what you may and may not do: if you violate the terms, you do not have permission to copy the software, and are liable for copyright infringement. One limit on the terms is that they cannot take away a right that you already have by copyright law (e.g. "fair use" cannot be negated by a license term). Another limit is that the terms have to be consistent with contract law, hence the license cannot include a human centipede obligation – or, "all your stuff belong to us". When a contract is ambiguous, the ambiguity is construed against the writer, and that is also so with software licenses. Also like the situation with contracts, the terms have to be legal, that is, cannot deny some right or requirement encoded in law. There is a legal requirement that disclaimers have to be "prominent", and that holds of license terms.
As for "tricking" a person, that's not supposed to happen, with a proper license. If you put stuff out there and say nothing, nobody has been given permission to copy the item. You can make it available to a specific named person, but that is limited to one person, thus a license includes language allowing anyone to copy, but also requiring that the license be retained with any subsequent copies. Hence B copies from A, and sees the license; B may share with C (assuming a decent license) but must include that or substantially equivalent license; and so on. A problem arises if B redistributes without original license, substituting a bogus license. When C copies, that copying is not done with the permission (implied or express) of A, and C could be open to legal consequences. B is also clearly open to consequences, since re-distribution with the self-perpetuating license is a violation of the terms of A's condition grant of permission.
Ignorance of the true ownership of copyright is no excuse, and there is no general innocent-infringement exception to copyright law in the US. However, the part of copyright law that talks about remedies for infringement, 17 USC 504(b)(2) lessens the burden on the innocent infringer:
In a case where the infringer sustains the burden of proving, and the
court finds, that such infringer was not aware and had no reason to
believe that his or her acts constituted an infringement of copyright,
the court in its discretion may reduce the award of statutory damages
to a sum of not less than $200.
Still, not zero.
I don't see how adding some NOPs would make it impossible to prove that you have a copy of someone else's IP. Perhaps it's not a trivial, but still quite possible.
