HSBC has become the latest target of global cyberattacks on banks that prevent customers using their online services, according to the London-based bank.
The bank said yesterday that HSBC servers came under a denial-of-service attack that hit several of its websites around the world but did not affect any customer data.
"We are taking appropriate action, working hard to restore services," the bank said in a statement. "We are pleased to say some sites are now back up and running."
By 10am Hong Kong time, all HSBC websites globally had returned to normal.
Yesterday morning, the South China Morning Post found HSBC websites in some countries were inaccessible.
They included Britain, Pakistan, Ireland and Russia.
"We apologise for any inconvenience caused to our customers throughout the world," HSBC said. The Hong Kong Monetary Authority said HSBC had notified it about the attack and was preparing a detailed report.
The authority said: "We will study the report and follow up with the bank if and when necessary."
Hong Kong police said they had not received a report so far. "We are now studying the matter to elicit more information," a spokesman said.
Roy Ko Wai-tak, manager of the Hong Kong Computer Emergency Response Team Co-ordination Centre, said it appeared the HSBC website in Hong Kong was not affected by the attack. He said the campaign of denial-of-service attacks started in the US late last month.
Capital One Financial and BB&T in the US were also targeted in yesterday's attack.
A group calling itself Izz ad-din al-Qassam Cyber Fighters claimed responsibility in statements posted to the website pastebin.com
The group said the attacks were in response to a video uploaded on YouTube that ridiculed the Prophet Mohammed and offended Muslims.
Ko said that denial-of-service attacks had become more popular in the past year or so.
"The aim is not to gain access to computers to steal data," he said. "Rather, such attacks make targeted computers and websites unable to operate normally."
Hong Kong police said such attacks were an "emerging trend in technology crime".
There were 23 reported attacks of this type in the first half of the year. Sixteen of the 23 attacks were aimed at financial companies.
"Most of the attacks came from overseas," a police spokesman said.
Police will set up a cybersecurity centre by the end of the year to combat the rising number of technology crimes.
Additional reporting by Lai Ying-kit