Mr. Nobody, does your router have a firewall security log? If it does, check to see the security events on the day this happened. Some routers will trigger a security event after a DoS attack, which could conclude where the attack came from. However, if it was a DDoS attack there will be no way to prove where it came from. I still believe that it is fairly likely that Fen was the culprit given the situation. It would just be nice to see if there is any additional evidence available.