Availability ensures systems and data are accessible when needed. Threatened by: DoS/DDoS, hardware failure, natural disasters, ransomware, misconfigurations. Improved by: redundancy, DRP, clustering, backups.
CIA triad: Confidentiality (prevent unauthorized access), Integrity (prevent unauthorized modification), Availability (ensure access when needed). ICS/SCADA prioritizes availability. DDoS attacks target availability specifically.