The Information Commissioner's Office (ICO) has warned web users about the risk of posting personal details online after a study found that the amount of digital information stored about us will grow by a factor of ten between now and 2011.

The amount of personal information digitally created and stored reached 281 exabytes in 2007 - that's 281 billion gigabytes, enough data to fill more than 1.5 billion iPods. That figure is expected to grow at an annual rate of 60 per cent per year over the next five years, a study by IDC, the research firm, suggests.

About a half of that is personal information such as photos and videos uploaded worldwide to sites such as YouTube and Flickr, or stored within PCs. The remainder is information captured elsewhere, such as on surveillance cameras, in company records, and in medical databases.

The "broad forces" propelling the growth in the explosion of personal information, the study's authors said, were mobility, increased interactivity through the internet, and "storage, storage, storage" - a reference both to the advent of services that store photos and other material online, and the growth of external hard drives for backing up memory on computers.

But while the authors of the report, called The Diverse and Exploding Digital Universe, saw this as proof that people were now "coming to understand the need to preserve their information heirlooms," the ICO reminded consumers about the dangers of failing adequately to protect themselves against identity thieves.

"The more personal information that is collected and stored, the greater the risks that some of that information will be wrong, out of date or will end up in the wrong hands," David Smith, the deputy information commissioner, said. "Some individuals are posting content on social networking sites without thinking about the electronic footprint they leave behind. It is important that individuals consider this when putting information online.

"It is equally important that websites also take some responsibility. In particular they should ensure that personal information is not retained for longer than necessary especially when the information relates to a person who no longer uses the site."

According to IDC, the majority of digital information stored about us is in the form of either video or photos taken by digital cameras, of which more than a billion have now been sold globally.

"Within five years, there will be two billion people on the internet, and three billion mobile phone users," the study's authors wrote. "All will be interconnected, all will be creating and consuming content at an alarming rate. To deal with so much change, IT organisations are going to have to create new policies for information security, and face the public if data is lost, breached or compromised."

A majority of people also still failed to understand that there were significant security risks associated with social networking sites, and that content they placed online remained there permanently, storage experts said. "Despite the fact that there are now mechanisms for controlling what remains private, many people don't understand that while it might be fun for one audience to see pictures of you drinking, it's not appropriate that they be seen by a potential future employer," Andrew Reichman, a senior analyst at Forrester, said.

The last couple of years have witnessed an explosion in the amount of devices and online services that are capable of storing information, from external hard drives for PCs which can now hold up to two terabytes - 2,000 gigabytes - of information, to web-based e-mail accounts like Gmail, which offer up to ten gigabytes of storage free.

"One of the consequences is going to be that we spend much more time searching through all this information to find stuff than we used to," Mark Margevicius, a research analyst at Gartner, said. "The whole way we think about data is going to have to shift dramatically - for instance by using meta-tagging [the process of assigning 'catchwords' to content so that it can be found more easily]."

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