HSBC has restored its online banking services after a distributed denial of service(DDoS)attack.
HSBC said servers had come under a DDoS attack which affected HSBC websites around the world.
The DDoS attack on HSBC did not affect any customer data,but did prevent customers using HSBC online services,including internet banking.
"We are cooperating with the relevant authorities and will cooperate with other organisations that have been similarly affected by such criminal acts,"HSBC said.
In May,internet security firm Check Point said a survey of 2,500 IT professionals worldwide found DDoS attacks comprised one of the top risks to their networks.
Check Point said organisations need to be able to collaborate and share intelligence on emerging threats,so the severity of attacks can be mitigated or even blocked.
In April,a study revealed financial services firms were targeted by three times as many DDoS attacks in the first quarter of 2012 than in the previous three months.
This represented a 25%increase compared with the same period in 2011,according to the Q1 Global DDoS Attack Report from security firm Prolexic Technologies.
A report form the Ponemon Institute found DDoS attacks were among the most costly cyber attacks on UK organisations alongside those caused by malicious insiders and malicious code,according to the 2012 Cost of Cyber Crime study by the Ponemon Institute.
UK and Australian organisations were also found to be the most likely to experience DoS attacks,while German companies were the least likely target.
Attackers commonly use DoS to blackmail large organisations that depend on online availability to conduct business.
In July,Chinese and Hong Kong Police arrested blackmailers threatening commodities and securities traders with DDoS attacks.
The gang had demanded 3,000 to10,000 from 16 Hong Kong-based firms and threatened to cripple their online operations with DDoS attacks if they did not pay.
