How Screensavers Work

Here's exactly what it does:

1. To find out whether it can start the screensaver or not, Windows sends a message to the foreground application. This command is asking the application, "Can I start the screensaver?" A non-Windows program will not understand the command, and therefore will not answer it. A CBT application will understand it, but will respond with a command that means "No, I'm providing training right now." All other applications should respond positively to the command.

2. Windows then looks at the line SCRNSAVE.EXE=____ in the system.ini file to see if a screensaver has been specified. If the entry is blank, it ignores the command to execute the screensaver. But if a filename is listed, it attempts to load that file. As long as the file listed is an actual screensaver, the program executes and creates the screensaver images on top of the current desktop.

3. The screensaver continues to run until Windows detects input from the keyboard or mouse. With most screensavers, moving the mouse or pressing any key will immediately terminate the screensaver. But screensavers can be programmed to stop when only certain keys or buttons are pressed, or when the mouse is moved a certain distance. This feature is especially useful in interactive screensavers.

4. When Windows gets input that it should terminate the screensaver, it checks to see if password protection is turned on. If it is, a box pops up requiring that you enter a user name and password. Otherwise, the screensaver simply terminates.

When password protection is active, failure to supply the correct name and password will cause Windows to continue to run the screensaver program. While this provides some security, it is important to note that Windows 95/98 screensavers create their own password dialog boxes, and request the password and user information from the system. If you are not certain of the reliability of the source of the screensaver, be careful about using password protection. Hackers can and do create screensavers that use this weak point in system security to capture passwords. This is not an issue with systems running Windows NT, which only allows screensavers to call up the system password dialog box -- they can not create their own.