NEW YORK — Russian hackers have stolen 1.2 billion user names and passwords in a series of Internet heists affecting 420,000 websites, according to a report published Tuesday.

The thievery was described in a New York Times story based on the findings of Hold Security, a Milwaukee firm that has a history of uncovering online security breaches.

Hold Security didn’t immediately respond to inquiries from The Associated Press.

The identities of the websites that were broken into weren’t identified by the Times, which cited nondisclosure agreements that required Hold Security to keep some information confidential.

The reported break-ins are the latest incidents to raise doubts about the security measures that both big and small companies use to protect people’s information online.

Security experts believe hackers will continue breaking into computer networks unless companies become more vigilant.

“Companies that rely on usernames and passwords have to develop a sense of urgency about changing this,” Avivah Litan, a security analyst at the research firm Gartner told the Times.

Retailer Target Corp. is still struggling to win back its shoppers’ trust after hackers believed to be attacking from Eastern Europe stole 40 million credit card numbers and 70 million addresses, phone numbers and other personal information last winter.