A Russian crime ring has amassed the largest known collection of stolen Internet credentials, including 1.2 billion user name and password combinations and more than 500 million email addresses, security researchers say. 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.