Australian businesses are losing money at a skyrocketing rate to cyber security threats, as the nation's top cyber spy agency warns of mounting ransomware and identity fraud risks.

Cybercrime reports have dropped but businesses face a bigger financial impact from them, the Australian Signals Directorate's annual cyber threat report reveals.

The average cost of cybercrime to large businesses was $202,700 in the past financial year, up 219 per cent on the previous year, and an average of $97,200 for medium-sized businesses, up from 55 per cent, the report published on Tuesday shows.

The average cost of cybercrime for small businesses was $56,571.

The directorate received 84,700 reports of cybercrime over the past financial year, down three per cent on the previous 12 months.

The agency'

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