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In windows XP and windows Vista, Microsoft still enforce and limit the maximum simultaneous half-open outbound TCP connection attempts per second that the system can make in order to protect the system being used by malicious software, such as viruses and worms, to spread to uninfected computers, or to launch distributed denial of service attack (DDoS).

The number of TCP connection attempts are limited differently by different version of windows. For example, windows XP SP2 has 10 maximum incomplete concurrent connections attempts limit per second, Windows Vista Home Basic has maximum limit of 2 and Vista Ultimate has 25 per second.

This is why heavy P2P (peer-to-peer) applications such as uTorrent, BitComet, Thunder, eMule, etc, or P2PTV such as PPLive, PPStream, Sopcast, etc may face some error or slow download and upload speed due to these limitations.

However there are some some tools to fix or to crack the TCP concurrent connection limit in Windows XP, Vista & 7.

Although any patch for tcpip.sys to remove or increase half-open outgoing TCP connections limit is no longer required now, as the half-open TCP connections is unlimited by default in Windows Vista and Windows Server 2008 SP2, and Windows 7, some users who still using Windows Vista Starter, SP1 or RTM, Windows XP or Windows 7 beta may still in the restriction of half-open TCP connections.

Universal Tcpip.sys Patch (UTP) support almost all versions of Winodws operating system. According to the author of Universal Tcpip.sys Patch, the supporting OS are Windows XP/2003/2008/Vista/Windows 7, All SP*, All 32bit (x86) / 64bit (x64).

Download Universal Tpcip.sys Patch

Current Version : 2009.04.09 V1.2.0.12
Download Link 1: UniversalTcpipPatch_20090409.zip
Download Link 2: UniversalTcpipPatch_20090409.zip
More Information: UniversalTcpipPatch

As shown in the screenshot, Universal Tcpip.sys Patch shows the information to ensure that users know if the tcpip.sys file has been patched properly or not.

The meaning of the last number of checksum:
1 - Original file, without any modification.
3 - The file has been modified, but with a test certificate.
9 - The file has been modified, but not repair signing.
Windows XP does not compare the signing, don’t worry.