For the US Securities and Exchange Commission, Jan. 15, 2019, was a day of redemption. The agency filed one of its highest-profile enforcement cases in years, capping the work of two dozen staff across five divisions.The case, recounted in a 43-page complaint, read like an airport potboiler: Ukrainian cybercriminals had infiltrated a vast computer network containing soon-to-be-published earnings reports for some of America’s biggest companies, then sold the information to a shadowy web of trader...