Prior to version 8, access control is not turned on in X-Win32. Any application wishing to connect to the X server can do so without interacting with the user. This represents a significant security concern. To prevent any users from connecting to your X server, you should enable access controls in X-Win32. To do this:

  1. Right-click on the blue X icon near the clock.
  2. Select XConfig from the menu by clicking on it
  3. Click on the Security tab
  4. Make sure that both “Access Control” and “Use XAuth” are checked
  5. Click “Apply,” then “OK”

After doing this, any future connection to the X server will present you with a dialogue box similar to the following:

As a general rule, you should only accept connections that you have initiated and expect.