The Royal Bank of Scotland's internet payment division WorldPay has been hit by a distributed denial of service (DDOS) attack, affecting thousands of its customers.

Cyber-criminals are believed to have launched the attack using hundreds of virus compromised 'zombie' computers, but WorldPay declined to confirm whether it was part of an attempt to extort money from the banking offshoot.

WorldPay customers started noticing severe delays to the service on Saturday, when the DDOS attack started to flood its networks.

The company's payment and administration systems still remain affected today, with transactions taken longer to process than usual.

'We can confirm that WorldPay has been subjected to a distributed denial of service attack, a malicious act which has systematically flooded our networks,' said a WorldPay spokesman.

'Our ability to deliver service to customers has been adversely affected as a result and we apologise unreservedly to our customers for any inconvenience.'

WorldPay says that it has taken 'swift corrective action' since the attack started and that services remained secure.

'Owing to the criminal nature of this act, the relevant authorities have been informed and WorldPay will co-operate closely with them,' the spokesman added.

WorldPay experienced a similar attack in November last year, while online bookmakers were the victims of a DDOS Russian extortion gang in spring.

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