Just when journalism is under attack for its use - and misuse - of anonymous sources, along comes the most famous unnamed source of all to highlight the importance of this reporting method.
This week, the Washington Post confirmed that "Deep Throat" - the mysterious figure who informed the newspaper's Watergate investigation - is W. Mark Felt, the FBI's No. 2 during the scandal that brought down President Nixon in 1974.
That the mutual pact of anonymity held for over 30 years - withstanding intense political pressure and even the investigative prowess of a university journalism class - is remarkable.
It testifies to the fidelity to secrecy necessary between reporters and some sources, especially whistle-blowers.
Many other factors, including Senate hearings, White House tapes, and even named sources, helped the Post expose the politically motivated burglary of Democratic headquarters at the Watergate building, and its subsequent coverup by the Nixon administration. But Mr. Felt's role as a well-placed informant who could guide the reporters and confirm their findings was integral to their work.
The media do rely too heavily on anonymous sources, which have the negative side effect of undermining a story's credibility. Reporters should strongly urge sources to talk on the record.
But there are some cases, such as when the greater public good is at stake or the law is being flouted, when a source can't talk openly. This was one of those cases.