The Microsoft .NET Framework 1.1 Service Pack 1 is a roll-up of all reported issues found in the release version of the Microsoft .NET Framework 1.1. SP1 also offers some new notable improvements such as Data Execution Prevention, greater protection from buffer overruns, support for the security enhancements in Windows XP Service Pack 2 as well as better support for consuming WSDL documents.

The .net framework 1.1 SP1 also fixes a really annoying issue that a lot of home users find themselves in after installing the 1.1 framework from Windows Update. What is that issue I hear you ask? Simple, the framework install creates another user account so it can run the ASP.net worker process for Internet Information Services under a restricted user account for enhanced security. This in itself is not a bad thing, but in the first version of the 1.1 framework this user prevented the system auto logging on to the desktop. A change was made to further hide the user account and under SP1 there is no longer an auto logon issue.

Download the .Net Framework 1.1 Service Pack 1 (10.4Mb)
http://www.microsoft.com/downloads/details.aspx?
FamilyID=a8f5654f-088e-40b2-bbdb-a83353618b38&DisplayLang=en

Issues Resolved in the 1.1 Service Pack
http://msdn.microsoft.com/netframework/downloads/updates/
sptechpreview/content11sp1.aspx

What is the ASP.NET Machine Account?
http://mvps.org/marksxp/WindowsXP/aspdot.php