Three Republican senators are demanding answers around Alphabet Inc.-owned Google’s decision to hide a security vulnerability that exposed the private information of at least 500,000 users of its little-used social network, Google+. The letter, from Sen. John Thune, who serves as the chairman of the Commerce Committee, and senators Roger Wicker and Jerry Moran says it was “troubling” to learn of an internal memo that circulated inside the company, urging Google to hold off on announcing the…