public void AddWriteRightsToEveryone(string filename) { // get sid of everyone group SecurityIdentifier sid = new SecurityIdentifier(WellKnownSidType.WorldSid, null); // create rule FileSystemAccessRule rule = new FileSystemAccessRule(sid, FileSystemRights.Write, AccessControlType.Allow); // get ACL of file FileSecurity fsecurity = File.GetAccessControl(filename); // modify ACL of file fsecurity.Add(rule); // apply modified ACL to file File.SetAccessControl(fileName, fSecurity); }