Encryption technology used by Apple's iMessage makes it "impossible" for law enforcement to intercept the content of those messages, according to documentation from the Drug Enforcement Agency (DEA).

As reported by CNET, the DEA released an unclassified document that discusses how iMessage might thwart criminal investigations.

The DEA's San Jose office discovered last month that iMessages sent between Apple devices "are not captured by pen register, trap and trace devices, or Title III interceptions," the document says. "iMessages sent between two Apple devices are considered encrypted communication and cannot be intercepted, regardless of the cell phone service provider."

It's easier to intercept a message between an iOS and non-iOS device, the DEA said.

Apple introduced iMessage in 2011. By Nov. 2012, messaging data tipped a decline in text messaging for the first time in western markets - due in part to the switch to iMessage.

While you might find it heartening to learn that the feds cannot monitor the iMessages on your iPhone, the issue complicates efforts to collect evidence against those who are using their Apple gadget for criminal activity.