One week after Alex Holden said he found “arguably the largest data breach to date,” he doesn’t want to argue semantics. Holden, founder of Hold Security, gained a measure of fame last week when he said he had obtained 1.2 billion unique online credentials from a Russian gang. Some competitors and independent experts questioned the scope of his claim. It was unclear, they said, how much of Holden’s data came from previously known breaches or included old, invalid passwords. Just as unclear was how much data the Russian hackers had stolen themselves and how much they had collected from others. “What’s a breach?” Holden asked in a phone interview Tuesday. “I don’t want to get into the semantics of ‘What’s a breach?’ ” Answers to some questions may be unknowable – the share of data from new breaches, for example. “Everything was not fresh,” Holden said.