Michelle Zatlyn, 44, was on the virtual frontlines. Within 12 minutes of the initial rocket assaults, the San Francisco-based company she co-founded, Cloudflare, detected and began mitigating attacks from hackers, presumed to be state actors, as well as civilians and so-called hacktivists, according to legal experts. In the weeks that followed, the company, which provides cybersecurity services to about 20 percent of the world’s websites, automatically identified and stopped DDoS attacks that amounted to five billion site requests.