Multiple US Navy personnel say they've received potentially malicious smartwatches in the mail

The US Naval Criminal Investigative Service is investigating after multiple Navy personnel reported receiving unsolicited smartwatches in the mail that could be installed with data-stealing malicious software, an NCIS spokesperson told CNN on Friday.

The news comes after the Army warned publicly this month that "service members across the military" had reported receiving the devices in the mail.

It's unclear who is mailing the suspicious watches, but the devices are telltale signs of a counterintelligence and cyberthreat. When used, the devices automatically connected to wireless networks and cell phones, "gaining access to a myriad of user data," the advisory from the Army's Criminal Investigation Division (CID) said.

The watches may also contain malware that would "grant the sender access to saved data to include banking information, contacts, and account information such as usernames and passwords," the advisory said.

"Smartwatches, like any wearable device, can be used by adversaries to gain a wide collection of personal information and pose a security threat to U.S. Navy and U.S. Marine Corps service members," NCIS spokesperson Jeff Houston told CNN in an email, adding that service members receive counterintelligence training to deal with such situations.

The scope of the US military's exposure to the suspicious watches is unclear. Houston declined to comment on how many Navy personnel received the watches, or who might be mailing them, citing an ongoing investigation.

A spokesperson for the Army CID referred questions on the advisory to the Air Force Office of Special Investigations, which did not respond to requests for comment.