The government said there was no indication that the data had fallen into criminal hands. But technology experts and civil libertarians said the lapse highlighted the risks associated with providing personal information to governments and large institutions.
Other security experts described it as potentially the most significant data breach of the information age. Treasury chief Alistair Darling, charged with disclosing the breach to lawmakers, called the event "catastrophic," The AP reported at the time.
"I can well understand people's anxiety and anger that this has happened. It should never have happened, and I apologize unreservedly for that," Darling said.
But British officials are not the only government representatives who have had to deal with data disasters.
In May 2006, U.S. Veterans Affairs officials disclosed that a laptop containing personal information for millions of veterans had been stolen in a burglary from the home of an agency employee in Maryland.
The agency estimated that about 17.5 million veterans were at risk and reportedly offered to cover the cost of monitoring their credit for one year, to the tune of $160.5 million.
Fortunately, about a month later, the FBI announced it had recovered the laptop and the personal information had not been compromised.
It started with an exploding laptop in Japan and ended with one of the largest electronics-related recalls the Consumer Products Safety Commission had ever seen.
After one of its computers caught fire at a conference in Japan, in August 2006, Dell recalled 4.1 million notebook computer batteries that were supplied by Japan's Sony Corp.
The flaming computer was caught on video and proceeded to go viral online, along with several other news reports and pictures of burning Dell laptops.
Though it is now eclipsed by this year's Heartland hack, a massive intrusion on T.J. Maxx's systems a few years earlier is significant because it was one of the first to show just how vulnerable retailers were.
In December 2006, T.J. Maxx alerted law enforcement that cybercriminals had stolen more than 45 million customer records in 2003 and 2004.
According to Information Week, within eight months, the company had spent more than $20 million investigating the incident, notifying customers and hiring lawyers to deal with the dozens of associated lawsuits. The hack alerted the industry to the threat of cybercriminals and pushed lawmakers to fast-track data security legislation, Information Week reported.
In August 2003, a massive blackout left more than 60 million customers in the U.S. and Canada without electricity. The cause? Some say a software bug in an Ohio utility's system was to blame.
The blackout started in Ohio, when fallen trees took down power lines managed by Akron, Ohio-based FirstEnergy Corp. But eSarcasm's Tynan said that, because a critical alarm did not sound, the problem spread to other parts of the country.
"A computer cascade. That's the reason all those failures happened," he said.
Testifying before Congress, Pete Burg, the chief executive of FirstEnergy, said, "We strongly believe that such a widespread loss of power could only result from a combination of events, not from a few isolated events."
But in an interview with InformationWeek, Stan Johnson, manager of infrastructure security at the North American Electric Reliability Council, said that if the alarm had gone off as planned, the blackout could have been contained.
"It didn't cause the power to go off, but it was a big contributor to the lack of response by FirstEnergy," Johnson said.