What are sleeper cells? Mystery radio transmission triggers US security warning

U.S. intelligence agencies have issued a nationwide alert after intercepting encrypted communication that is believed to have originated from Iran.

This sparked concerns that the encrypted message could point towards the activation of sleeper cells operating abroad.

A sleeper cell is a group of secret operatives or agents who are placed in a targeted country or organisation and are activated to perform specific missions after remaining inactive (asleep) for long periods.

The missions can be espionage, sabotage, terrorism, or any other covert operations.

As reported by ABC News, the alert was distributed to law enforcement agencies across the United States, prompting heightened vigilance.

The intercepted transmission is reportedly of the day when Iran’s Supreme Leader Ayatollah Ali Khamenei was killed.

Officials reported that the message was relayed through various countries and transmitted via shortwave radio using coded numbers.

Intelligence agencies send instructions to their undercover agents via these broadcasts, who then decipher the message with the correct encryption keys.

Without a proper cypher, it is nearly impossible to decode the message.

While the content of the encrypted message couldn’t be decoded, federal officials state that the appearance of a new international broadcast station using encrypted signals has triggered increased monitoring of suspicious radio-frequency activity.

The alert stressed that there is currently “no confirmed operational threat tied to a specific location,” but law enforcement agencies have been advised to remain on heightened alert.

U.S. counterterrorism officials say that investigations are ongoing to assess the exact origin and purpose of the mysterious transmission.

What is a cypher?

A cypher is a method of encoding messages to transform readable information (plain text) into a secret, unreadable format (ciphertext). Used for data security and to hide messages, cyphers typically involve substitution or transposition techniques.