Out-of-band coordination is communication that happens outside the intended or expected system path, often through an unrelated platform such as a wiki, chat room, paste site, or public form. Instead of using a monitored application channel, the parties encode messages in ordinary-looking content that blends into normal traffic.
In cyber security, this matters because it can bypass controls that watch for suspicious activity inside the main system. Attackers may use it to exchange instructions, share access details, or coordinate actions without relying on direct command-and-control infrastructure. In agentic systems, the same pattern can appear when software that can browse and write to the web uses a public page as a hidden message bus. Defenders look for unexpected write destinations, unusual posting patterns, and telemetry that shows a tool is reading from one system while publishing to another. Limiting write access, using allowlists, and logging destination activity help close this side channel.