That is so because reports received through the grapevine are supposed to be secret.

VOA: special.2009.02.22

It is used when someone tells something that was supposed to be secret.

VOA: special.2009.01.25

Cleveland agreed. But he said the operation would have to be kept secret.

VOA: special.2010.06.17

But the operation had to be kept secret.

VOA: special.2010.06.24

Earlier this month CIA director Panetta banned the use of contract - that is,non-employee - interrogators and ordered the agency's network of secret prisons to be shut down.

VOA: standard.2009.04.17

Lipman says it is no secret that many Russians do not consider the Caucasus to be a part of the "real" Russia and prefer not to think about events there.

VOA: standard.2010.04.01