I know it seems to be a very long joke, but in fact that's the IRS' legal position.

In April 2012, the [National Organization for Marriage] asked the IRS for an investigation [into who leaked their confidential donor information to their top political opponent, Human Rights Watch]. The inspector general's office gave them a complaint number. Soon they were in touch. Even though the leaked document bore internal IRS markings, the inspector general decided that maybe the document came from within the NOM. The NOM demonstrated that was not true.

For the next 14 months they heard nothing about an investigation. By August 2012, the NOM was filing Freedom of Information Act requests trying to find out if there was one. The IRS stonewalled. Their "latest nonresponse response," said Mr. Eastman, claimed that the law prohibiting the disclosure of confidential tax returns also prevents disclosure of information about who disclosed them. Mr. Eastman called this "Orwellian."

But 1984 was serious in tone -- this is so farcical it's more like Catch-22.

http://www.breitbart.com/InstaBlog/2013/06/10/IRS-We-Can-t-Tell-You-Who-Violated-Your-Privacy-Because-That-Would-Be-Violating-the-Privacy-of-Whoever-Violated-Your-Privacy