The US Air Force has opened an investigation into a "malware" infection – which it is blaming on lawyers employed by the US Navy who are working on a war crimes case.

The bizarre case hinges around an alleged attempt by a US Navy prosecutor to plant malware on the devices of US Air Force lawyers defending a US Navy SEAL over war crimes charges from his time commanding a small unit in Afghanistan.

Like the UK, US military lawyers can work on cases involving people from outside their own branch of the armed forces.

The US Air Force Times, an independent publication, quoted from a memo written by Captain David Wilson, a senior Navy defence lawyer, referring to "malware" found on the machine of a USAF lawyer he was working alongside. This was later described as having been written to gain "full access to his computer and all files on his computer".

"In fact, I've learned that the Air Force is treating this malware as a cyber-intrusion on their network and have seized the Air Force Individual Military Counsel's computer and phone for review," he wrote.

The malware was further described as "tracking software".

Similar malware was sent to the editor of sister publication the US Navy Times, USAF Times reported. The editor had written a number of detailed articles about the ongoing trial, leading USN prosecutors to believe someone was leaking documents – in breach of a court order. USAF Times speculated that the malware was sent in the hope of identifying potential sources for those leaks.

The paper claimed the email had "contained hidden computer coding designed to extract the IP address of the Navy Times computer network and to send that information back to a server located in San Diego".

If unauthorised, such behaviour would be a clear criminal offence under American law.

The intentional, weaponised use of malware by state agencies is something that is, by law and custom, restricted to being used against actual criminals and not journalists. While aggressive and unsupervised law enforcement bodies across the world do abuse their powers, break the law and spy on journalists, doing so with email malware appears to be a new one. ®