A garda investigation is under way into a number of cyber attacks on computer systems of small businesses and subsequent demands for money.

Criminals have been hacking into business systems, encrypting their data and demanding money for codes to unlock the information.

The Garda Bureau of Fraud Investigation is aware of extortion demands from companies in the midlands and west of the country and is investigating the cases.

The companies say their computer systems were hacked, their data such as order books and customer data had been encrypted and their businesses paralysed.

They told gardaí that there was a note left on their computers demanding money - in one case $700 for the code to unlock the information.

The Garda Bureau of Fraud Investigation has consulted specialists from the UCD Cybercrime Centre to help with the investigation.

Detectives say they believe the crime is being committed from outside the country, the amounts demanded are small, and businesses without adequate security systems are being affected.

They are asking companies that have been targeted to contact gardaí.