An adjective for a secret that is known to a third party

I am writing some text for a piece of software and am stuck with this sentence:

Use this function if you think that your private key has become known to a third party.

While the sentence explains very well when you should use a specific function, I take issue with the last part has become known to a third party. I feel that it's too long and not good enough to emphasize what I mean.

I have been looking at compromised, but that means that the situation happened because of indiscreet, foolish, or reckless behavior (Oxford American Dictionary), which might not be the case.

I also gave leaked a try, but that has the connotation that something was knowingly published to a broader audience, which is not what I am looking for.

What I am looking for is an adverb that explains exactly the situation, where a private key to access certain information was obtained by a third party, which can then use it for malicious purposes (they use it for themselves).

The use of compromised referring to encryption keys which can no longer be trusted is something that has been used pretty commonly. If a third party has obtained a secret key something indiscreet has almost been guaranteed to have happened. Changing the phrase to "private key has been compromised" is short and to the point.

Given the context, I think compromised is an excellent choice.

Per this answer, compromised is the best choice. If that is not acceptable, you could also say that the private key has been exposed.

I understand your reasons for rejecting compromised, but I think it is the most common expression for this instance.

Since compromise won't suit, you might consider expropriated, which means "to take (something) from another's possession for one's own use."