As part of advanced callback protection, Sensors can protect your network from attacks effected through a Fast Flux Service Network (FFSN). Typically, an FFSN is used for DDoS, spam, phishing, advanced malware attacks. Sensors use a heuristics-based detection mechanism to identify domains and IP addresses related to FFSN. Once Sensors identify the FFSN domains, they can detect the bots in your network, when they communicate with those FFSN domains.
Note
Because it is a heuristics-based detection mechanism, FFSN detection is equally effective in SPAN, tap, and inline modes.