A distributed denial-of-service attack shut down some of HSBC's online portals yesterday, 19 October, after the bank's website was targeted by attackers.

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Customers who use online banking were unable to access their accounts after the attack started at around 17:45 BST.

Users who were having difficulties soon took to Twitter to voice their concerns:

"HSBC down. http://www.us.hsbc.com , http://www.hsbc.co.uk & http://www.offshore.hsbc.com all offline. Looks serious. Anyone else seeing this?" tweeted Mark Denne, a partner in US firm West Avenue Capital.

A statement from HSBC followed shortly, explaining that the banking firm was doing everything possible to resume normal service:

"On 18 October 2012 HSBC servers came under a denial of service attack which affected a number of HSBC websites around the world. This denial of service attack did not affect any customer data, but did prevent customers using HSBC online services, including internet banking," the company said in a statement.

The bank later added: "We are taking appropriate action, working hard to restore service. We are pleased to say that some sites are now back up and running."

The company was also quick to assure customers that none of their account data had been leaked, tweeting: "Denial of service attack impacts some HSBC websites. No customer data or accounts affected. Working hard to restore service. Apologies again."

The site is now fully functional again, after the problems were resolved at 3am this morning, 19 October, nine hours after the attack started.

DDoS, or distributed denial-of-service attacks are an effective way of taking down a website, by flooding it with more page views and web traffic than the site's servers can handle. Hacker collective Anonymous is infamous for targeting several high-profile companies with DDoS attacks.

However, denial-of-service attacks are quickly becoming a widespread form of corporate sabotage, with various hackers and hacking firms offering to take down websites for a fee.

A report from IBTimes UK found that criminals will bring down a website for as little as $5 (£3) an hour.

A report on denial-of-service attacks, titled Denial of Service Attacks: A Comprehensive Guide to Trends, Techniques, and Technologies, claims that:

"DoS attacks have become industrialised, and can be purchased as a service from professionals. You don't need to be a hacker or part of an ideological movement to want to take down a site. Today, all you have to do is pay someone who'd take it down for you, for as much time as you like (and are willing to pay for)."

HSBC Twitter