FBI officials last week arrested a Russian computer security researcher on suspicion of operating deer.io, a vast marketplace for buying and selling stolen account credentials for thousands of popular online services and stores. Kirill V. Firsov was arrested Mar. 7 after arriving at New York’s John F. Kennedy Airport, according to court documents unsealed Monday. Prosecutors with the U.S. District Court for the Southern District of California allege Firsov was the administrator of deer.io, an online platform that hosted more than 24,000 shops for selling stolen and/or hacked usernames and passwords for a variety of top online destinations. …

Read MoreFBI Arrests Alleged Owner of Deer.io, a Top Broker of Stolen Accounts