What triggers Configurations.plist.signed ?

In ~/Library/Safari/ a file gets created that contains Google, Yahoo and Bing search "settings" that appear to come from http://configurations.apple.com/configurations/internetservices/safari/Configura tionsMac-5.0.4.plist.signed but I can't tell what causes it to be created or modified. Our managed clients w/PHDs were communicating continuously with this site across several days before calming down yesterday.