When it comes to being run, I don't think there are too many that provide actual services because it's a lot of work to keep the secrecy going for long. Consid

When it comes to being run, I don't think there are too many that provide actual services because it's a lot of work to keep the secrecy going for long. Consider the story of Crypto AG, the most enduring and therefore successful example of this sort of exploit; crucial for putting it in place was that the founder happened to be friends since 20 years with a highly placed chief in the NSA and that's just not a scalable model. It also required convincing an independent, world renowned, crypto expert to completely compromise their work and serve as the authority that kept lesser experts from questioning the cooked algorithm, also not a terribly scalable thing.