Anonymous sources are covered quit a bit in journalism school. At least they were in the school I attended. It's important that young journalists get it right. Because getting it wrong can lead to disasters in reporting and the credibility in the media takes the hit.
Most recently, CNN, is experiencing blowback as the result of relying on ONE anonymous source to run a story that could have had disastrous implications for the subject of the story--if only it were true. It turned out to be a lie. A lie perpetrated by the journalist or the anonymous source, no one knows for sure. The three journalists in question have since resigned, and the story was retracted.
The Society of Professional Journalists have set the standard for how to use anonymous sources. You can read about it HERE.
Anonymous sources are sometimes the only way journalists can truly be the watchdog of society. But before using a source who refuses to go on the record you must consider the source. Consider why they'd want to speak with you and consider the ramifications. Above all else, use that source to start investigating and looking for the truth. NEVER rely on one source and ALWAYS find evidence to back up the sources claims.
Many journalist today want to point to and defend their use of anonymous sources by pointing to Watergate and Woodward and Bernstein's work for the Washington Post that brought down Nixon. The problem is, journalism today is light years away from journalism 40 years ago.
With the nature of our 24 hour news cycle many articles are published without due diligence, meaning, they never follow up on leads and instead, run with stories with questionable accuracy. Because of that, much of what we see and read should be handled delicately without committing it to fact. Many times we must look for the facts ourselves. Question everything.
The Watergate stories relied on a whistleblower codenamed, "Deep Throat," and he never gave the journalist new information. He refused to give them anything confidential. Instead he would acknowledge the accuracy of what the journalists already had and if they were stuck, he'd give them names of people to interview. It was real journalism and nothing was published on the word of one guy. They were highly criticized for their use of anonymous sources and rightfully so. (Source) In political journalism we've devolved into a kinda trust us type journalism. In an age where many journalists involve themselves into the story, and include their own opinions, they are losing the watchdog mentality and have begun to attack down party lines.
WAYS TO SPOT BAD ANONYMOUS SOURCES
-Anonymous sources that offer "opinions of others"
-No description of the anonymous source-One should be provided without identifying
-Anonymous Sources that describe the nature or tone of a meeting
Bottom line? Read and verify and if you can't fully verify, take everything you read with a grain of salt. Anonymous sources are allowed too often and although sometimes they are needed, we need to lobby media to reduce it's use of anonymous sources.
ADDITIONAL ARTICLES TO REVIEW
The Disconnect of Anonymous Sources. Read HERE
When Unamed Sources are Flat Wrong. Read HERE
Deep Throat, turned out to be FBI Associate Director Mark Felt.