In Windows XP SP2/SP3 and Vista, Microsoft enforces and hard-limit (hard coded in tcpip.sys) the maximum simultaneous half-open (incomplete) outbound TCP connection attempts per second that the system can make, in order to protect the system from being used by malicious programs, such as viruses and worms, to spread to uninfected computers, or to launch distributed denial of service attack (DDoS).

But this may have affects applications, servers and p2p programs that attemp to open many outbound connections at the same time. To remove maximum concurrent half-open connection limits in Windows XPSP2/SP3 and Windows Vista, apply the patched with the following steps: