For Tanguy de Coatpont, head of the French and North African divisions of Kaspersky Lab, a computer security company, it is "the biggest in history involving a single company".
Michael Bittan, a risk manager at Deloitte, cautioned that it was "the biggest to be made public. There have possibly been others that were bigger".
At any rate, it is far from the first, and here are other notable major corporate hacks of recent years:
US retail giant Target was hit by a computer attack in December 2013 that affected 110 million clients. Seventy million might have lost personal data including names, addresses, phone numbers and e-mail accounts, while 40 million bank accounts and credit cards were also put at risk.
In January 2014, South Koreans scrambled to stop money being siphoned from their bank accounts after it emerged that data on 20 million credit cards had been stolen over several years.
The data was swiped by an employee from the personal credit ratings firm Korea Credit Bureau, who then sold it to telemarketing companies.
In August 2014, online data protection firm Hold Security claimed that Russian hackers had accessed 1.2 billion passwords linked to 420,000 internet sites around the world, from corporate giants to individual accounts. Hold Security pointed to a group of hackers called "CyberVor", which it said had potentially gained access to 500 million e-mail accounts.
In August 2015, hackers calling themselves The Impact Team published nearly 30 gigabytes of files including the names and credit card data of people who had signed up with Ashley Madison, a website for those who wanted to have extra-marital affairs.
The company's boss stepped down as several suicides were linked to the revelations.
READ MORE: Russian hackers attack US: reports
Ashley Madison had earlier offered to delete users personal data for a modest fee, but did not, resulting in the launch of a class-action lawsuit estimated at Can$760 million (US$578 million).
In September 2015, computer security experts discovered a virus dubbed "KeyRaider" that targetted Apple iPhones and iPads, and which had already affected 225,000 Apple accounts.
The virus intercepted communications with Apple's iTunes music store, stealing information as purchases were made. Users in 18 countries were affected.