Experts challenge Yahoo’s assertion that state-sponsored hackers were behind a 2014 breach that resulted in 500 million lost records.

Hackers are peddling roughly 427 million passwords belonging to users of MySpace, a social network that in its heyday was one of the most visited sites on the internet. The same service that claimed to have information on 164 million LinkedIn users earlier this month is now boasting to have information on 360 million MySpace...