The ABC has been targeted by an extensive campaign of malicious emails which took ABC News 24 off air temporarily on Tuesday morning.

The news channel had to be broadcast out of Melbourne after the Sydney system faltered.

The emails, which download crypto-ransomware, have also been sent to other public institutions, according to an internal staff email sent by the ABC director of technology Ken Gallacher.

“While initially targeting Australia Post customers, this activity has now been observed to be targeting a range of other organisations, including Telstra and Energy Australia,” the email said.

A spokeswoman for the ABC said: “There was an IT security issue this morning which affected some of the ABC’s broadcasting systems and created technical difficulties for ABC News 24.

“As a result we broadcast stand-by programming from 9.30am before resuming live news broadcasts from Melbourne at 10am. We are now operating normally.”

At least two different malicious emails were sent.