The records, discovered by Hold Security, a firm in Milwaukee, include confidential material gathered from 420,000 websites, including household names, and small Internet sites. Hold Security has a history of uncovering significant hacks, including the theft last year of tens of millions of records from Adobe Systems.
Hold Security would not name the victims, citing nondisclosure agreements and a reluctance to name companies whose sites remained vulnerable. At the request of The New York Times, a security expert not affiliated with Hold Security analyzed the database of stolen credentials and confirmed it was authentic. Another computer crime expert who had reviewed the data, but was not allowed to discuss it publicly, said some big companies were aware that their records were among the stolen information.
Hackers did not just target US companies, they targeted any website they could get, ranging from Fortune 500 companies to very small websites, said Alex Holden, the founder and chief information security officer of Hold Security. And most of these sites are still vulnerable. Mr. Holden, who is paid to consult on the security of corporate websites, decided to make details of the attack public this week to coincide with discussions at an industry conference and to let the many small sites he will not be able to contact know that they should look into the problem.
There is worry among some in the security community that keeping personal information out of the hands of thieves is increasingly a losing battle. In December, 40 million credit card numbers and 70 million addresses, phone numbers and additional pieces of personal information were stolen from the retail giant Target by hackers in Eastern Europe.
And in October, federal prosecutors said an identity theft service in Vietnam managed to obtain as many as 200 million personal records, including Social Security numbers, credit card data and bank account information from Court Ventures, a company now owned by the data brokerage firm
But the discovery by Hold Security dwarfs those incidents, and the size of the latest discovery has prompted security experts to call for improved identity protection on the web.
Companies that rely on user names and passwords have to develop a sense of urgency about changing this, said Avivah Litan, a security analyst at the research firm Gartner. Until they do, criminals will just keep stockpiling peoples credentials.
Websites inside Russia had been hacked, too, and Mr. Holden said he saw no connection between the hackers and the Russian government. He said he planned to alert law enforcement after making the research public, though the Russian government has not historically pursued accused hackers.
So far, the criminals have not sold many of the records online. Instead, they appear to be using the stolen information to send spam on social networks like Twitter at the behest of other groups, collecting fees for their work.
But selling more of the records on the black market would be lucrative.
While a credit card can be easily canceled, personal credentials like an email address, Social Security number or password can be used for identity theft. Because people tend to use the same passwords for different sites, criminals test stolen credentials on websites where valuable info can be gleaned.