500
Denial of service (DOS), distributed denial of service (DDoS), TCP SYN flood, buffer overflow, ICMP attacks, electrical disturbances (power spikes, electrical surges, power failure, blackouts, power sags, brownouts), system's physical environment attacks (temp, humidity, gas, etc)
What are Availability attacks?
NOTE: Availability attacks attempt to limit the accessibility and usability of a system. For example, if a attacker were able to consume the processor or memory resources on a target system, that system might be unavailable to legitimate users.