A zero-day fault is a vulnerability in the code that has not been detected, listed, or patched yet. Therefore, the FBI had zero days to respond to the attack. This is not the first time the hacker claimed breaching the FBI site. In 2011, CyberZeist is believed to have hacked the FBI site as a member of a group known as Anonymous.

Cyberzeist claims to have conducted the hack last month and has posted to Twitter what they claim are screen captures showing the FBI patching against the vulnerability, which appeared to permit public access.

After his most recent hack, CyberZeist asked his Twitter followers who would they most like to be his next hacking target, with 37.3% of respondents opting for banking corporations.