From Gizmodo:

An investigation carried out by Federal Communication Commission's own inspector general officially refutes controversial claims that a cyberattack was responsible for disrupting the FCC's comment system in May 2017, at the height of the agency's efforts to kill off net neutrality. The investigation also uncovered that FCC officials had provided congressional lawmakers with misleading information regarding conversations between an FCC employee and the Federal Bureau of Investigation's cybercrime task force. A report from the inspector general's office (OIG) released Tuesday afternoon states that the comment system's downtime was likely caused by a combination of "system design issues" and a massive surge in traffic caused when Last Week Tonight host John Oliver directed millions of TV viewers to flood the FCC's website with pro-net neutrality comments.

Investigators were unable to "substantiate the allegations of multiple DDoS attacks" alleged by then-FCC Chief Information Officer David Bray, the report says. "At best, the published reports were the result of a rush to judgment and the failure to conduct analyses needed to identify the true cause of the disruption to system availability." [Here's an excerpt from the report:] "While we identified a small amount of anomalous activity and could not entirely rule out the possibility of individual DoS attempts during the period from May 7 through May 9, 2017, we do not believe this activity resulted in any measurable degradation of system availability given the minuscule scale of the anomalous activity relative to the contemporaneous voluminous viral traffic."