High Quality Content by WIKIPEDIA articles! In computer networking, TCP Cookie Transactions (TCPCT) is an extension of Transmission Control Protocol (TCP) intended to secure it against denial-of-service attacks, such as resource exhaustion by SYN flooding and malicious connection termination by third parties. Unlike the original SYN cookies approach, TCPCT does not conflict with other TCP extensions, but requires TCPCT support in the client (initiator) as well as the server (responder) TCP stack.