SharePoint 2007: GetWebCollection (Webs.asmx) does not return webs based on a user permission

Supposedly in Webs.asmx web service we pass on the user credentials and then call GetWebCollection method to get the webs underneath the current site, we expect the web method to return only those webs for which the user has permission to.  But this web method actually returns all the webs present underneath the current site….