We observed machines under your control participating in a DDoS attack targeting Google IPs.

The attack was a UDP  amplification attack.  In this attack, a UDP-based service is abused to attack others, wasting your bandwidth and computing resources.  For more information about this style of attack, see https://www.us-cert.gov/ncas/alerts/TA14-017A

The participating IPs under your control are listed below, along with the port number abused, the start and stop times in UTC, and the approximate amount of data sent during that time.

Note that this is simply a misconfigured server, not an abusive customer or a compromised machine.