Fast-flux DNS

Fast flux is a DNS technique used by botnets to hide phishing and malware delivery sites behind an ever-changing network of compromised hosts acting as proxies. It can also refer to the combination of peer-to-peer networking, distributed command and control, web-based load balancing and proxy redirection used to make malware networks more resistant to discovery and counter-measures. The Storm Worm (2007) is one of the first malware variants to make use of this technique.

The basic idea behind Fast flux is to have numerous IP addresses associated with a single fully qualified domain name, where the IP addresses are swapped in and out with extremely high frequency, through changing DNS records.

Internet users may see fast flux used in phishing attacks linked to criminal organizations, including attacks on social network services.

While security researchers have been aware of the technique since at least November 2006, the technique only received wider attention in the security trade press starting from July 2007.

The simplest type of fast flux, named "single-flux", is characterized by multiple individual nodes within the network registering and de-registering their addresses as part of the DNS A (address) record list for a single DNS name. This combines round robin DNS with very short—usually less than five minutes (300s) -- TTL (time to live) values to create a constantly changing list of destination addresses for that single DNS name. The list can be hundreds or thousands of entries long.

A more sophisticated type of fast flux, referred to itself as "double-flux", is characterized by multiple nodes within the network registering and de-registering their addresses as part of the DNS Name Server record list for the DNS zone. This provides an additional layer of redundancy and survivability within the malware network.

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Wikipedia