Hackers gained access to several Iranian state television channels and broadcast pictures of an exiled dissident group, as well as a message saying Supreme Leader Ayatollah Ali Khamenei should be executed.
According to the state TV reports on January 27, the faces of Masud Rajavi and his wife, Maryam, were suddenly superimposed on a regular 3 p.m. news broadcast as a male voice chanted, “Salute to Rajavi, death to Khamenei."
The Mujahedin-e Khalq (MEK) is the main faction within the exiled opposition umbrella organization, the National Council of Resistance of Iran (NCRI). The opposition group, which has not taken responsibility for the attack, seeks to overthrow Iran's theocratic regime.
Masud Rajavi has not been seen in public in almost two decades and is presumed to have died. His wife, Maryam, now runs the MEK.
State broadcaster IRIB said in a statement that the hack lasted about 10 seconds.
"Our colleagues are investigating the incident. This is an extremely complex attack and only the owners of this technology could exploit and damage the back doors and features that are installed on the systems," IRIB Deputy Chief Ali Dadi told the state TV channel IRINN.
"Similar disruptions happened to the Koran Channel, Radio Javan and Radio Payam," he added, referring to other state-affiliated broadcast channels.
Iran has been targeted in the past by a series of cyberattacks such as one in October that disrupted the sale of heavily subsidized gasoline.
Iran has blamed such attacks on the United States and Israel.
The Islamic republic is due to kick off official celebrations early next month to mark the 43rd anniversary of the revolution that toppled U.S.-backed Shah Mohammad Reza Pahlavi.