GPL and Security Applications

It is no great secret that many intelligence gathering processes rely on the ignorance or carelessness of their targets.  That is why parties that engage in intelligence gathering are loathe to reveal the technical details of their tools.  If potential intelligence targets know the tools, they can know the limitations of those tools and take appropriate countermeasures.  Since law enforce and intelligence are (or at least should be) legitimate activities to preserve public safety, it is (arguably) in the public interest to protect information about "sources and methods."

So given that, is there a problem with using copyleft practices in an intelligence or security application?  Not really, at least not if you can trust your own customers to behave responsibly.  The key principle of copyleft open source software is that you must make your source code  available to the customers who receive your products.  That is not at all the same thing as making it available to the general public and even classified software can be copylefted if the license is drafted correctly.

For example, you could, in principle, produce classified software under a copyleft license and still be within the license and the law while delivering that software to a government customer within the same classified program.  You could, in principle, produce law enforcement products, not sellable to the general public, do so under a copyleft license and make the source code available only the the law enforcement agencies that actually buy the products.  Again, this can be fully legal and within the terms of the license.  The key concept here is that even though the end customer is free, under the license, to redistribute the work, they will do not so because of other practical and legal constraints outside of the license.  To be blunt, if you are being prosecuted for a national security violation, a lawsuit from a software vendor is the least of your worries.  Civil intellectual property law is not an appropriate tool for protecting state secrets anyway.