The attack was carried out through the abuse of memcached instances, taking the site down multiple times. On Wednesday, developer repository site GitHub was hit with a critical DDoS attack that took the site offline multiple times for a few minutes each time. According to a GitHub incident report, the attack peaked at 1.35 Tbps, followed by a second peak of 400 Gbps, which could make it the largest attack of its kind ever perpetrated. According to the incident report, GitHub was offline Wednesday from 17:21 to 17:26 UTC and intermittently unavailable from 17:26 to 17:30 UTC, thanks to the attack. The report noted that user data wasn’t at risk during the attack.
More information here.