Default Permissions for Shared Folders Is Read-Only Access for Everyone
Content provided by Microsoft
By default in Windows XP Service Pack 1 (SP1), if you click the Sharing tab of the Properties dialog box for the folder, and then share the folder for other users to access over the network, the folder has permissions that give everyone read-only access. In versions of Windows XP that are earlier than SP1, if you share folders by using the Sharing tab of the Properties dialog box, the folder has default permissions that gives everyone full control.
NOTE: This behavior is not true for folders that you share by using the New File Share Wizard and the Net.exe command. These folders continue to have default permissions that give everyone full control.
These changes to the default permissions settings are part of the security enhancements in SP1.