SAN FRANCISCO (AP) — Twitter at its best is a tool to get a message out quickly, efficiently and directly, whether you’re an activist or a local fire department. But it’s also a constant risk-and-reward calculation. A bombshell whistleblower report from Twitter’s former head of security alleges that the social media company has been negligently lax on cybersecurity and privacy protections for its users for years. The revelations could be especially concerning for those who use it to reach constituencies, get news out about emergencies as well as for political dissidents and activists in the crosshairs of hackers or other malicious actors.