Botnets frequently use DGA and fast-flux techniques to ensure the availability of their command and control (CnC) infrastructure. However, the CnC IP addresses are still exposed in plain-text in publicly available DNS A records, which can be exploited by defenders to disrupt botnet operations. This paper presents the concept of the IP Generation Algorithm (IGA) as a novel method, usable by botmasters, to encrypt the CnC IP address in DNS records to avoid plain-text IP address exposure. This raises the bar for blacklisting malicious IP addresses, and can also be combined with existing techniques to further harden the CnC. For use by defenders, an IGA botnet detection method based on the combination of DNS and NetFlow data is presented and validated using an emulated botnet and an ISP data set.