In cybersecurity, 'fast flux' is a technique used by cybercriminals to rapidly change the IP addresses or domain names associated with malicious websites, such as phishing or malware distribution sites. By constantly rotating DNS records, attackers make it difficult for defenders to block or take down these sites, as the underlying infrastructure is highly dynamic and distributed across many compromised computers (often part of a botnet). Fast flux can be used for both single-flux (rotating IPs for a single domain) and double-flux (rotating both IPs and name servers), increasing the resilience and longevity of malicious campaigns.