Blaming Russia – Not Hacktivists, Insiders or Incompetence – is easy for Yahoo to blame Russia. Security experts have long cautioned that attributions are political, not technical, in part because accurately tracing attacks back is notoriously tricky. Never attribute an attack to a nation-state, and if someone does, exercise caution. The Wall Street Journal reports Yahoo detected the attack – several weeks after it occurred – in the fall of 2014, believed that it had been launched from Russia. At the time, Yahoo also reportedly notified the FBI.”]
Source: https://www.cuinfosecurity.com/blogs/yahoo-breach-great-nation-state-cop-out-p-2260