The Drug Enforcement Administration has found it difficult to intercept text message conversations sent with Apple’s iMessage platform due to the encryption that Apple employs for it. According to internal documents a criminal investigation was hindered by the DEA’s inability to tap into iMessage conversations, despite the fact that they had a warrant. According to CNET, the DEA initially discovered that conversations that they had been collecting were incomplete.
The DEA's "Intelligence Note" says that iMessage came to the attention of the agency's San Jose, Calif., office as agents were drafting a request for a court order to perform real-time electronic surveillance under Title III of the Federal Wiretap Act. They discovered that records of text messages already obtained from Verizon Wireless were incomplete because the target of the investigation used iMessage: "It became apparent that not all text messages were being captured."
The good news here is that it’s difficult for just anyone to break into your iMessage conversations. iMessages are much harder to tap into than both phone calls and standard text messages. The FBI is currently in the process of amending a law requiring telecommunications companies to build in access points for surveillance, a law that does not currently apply to companies like Apple. For its part, Apple already states in the iTunes terms and conditions that they will share your data with the government if it became “reasonably necessary” to do so.