Microsoft has set in the past a default limit of 10 max half-open TPC connections in Windows, in order to protect users from malicious bots, spyware etc.
The problem is that p2p applications (e.g. torrent, eMule) require more half-open connections to function properly.
Windows XP Service Pack 3 (SP3) is installing a new version of the tcpip.sys file.
Therefore if you need to increase your max half-open connection limit, you will have to patch the file again.