I had been using a Guest account for a while and through it users were able to access a wireless network connection. The wireless connection was 802.11g WPA2-PSK AES. Users were able to boot the computer, login as Guest and access the Internet through this wireless connection. On October 15, 2010 a user booted and logged in as Guest but then discovered that they were unable to access any network connections (although a wired connection was not attempted). In attempting to resolve the issue I found that the Network System Icon was now missing from the Notification Area. In addition the Network and Sharing Center reported "Access is denied." To work around the problem I added a standard account for the user. Did a recent update to Windows 7 change the permissions of the Guest account so that it is no longer able to connect to a network? Test system: Windows 7 Professional x64

Thanks for the reply NTauthority local t.welch. Using "Windows Update -> View update history" I find that 19 updates were installed on October 14, 2010. The method you propose of removing the updates will likely help me narrow down the issue to the relevant update or updates but might take some time. I'll also take a look at the associated Knowledge Base articles for the updates to see if they mention this issue.