Under usual circumstances, java applets that are accessed on the internet are run within a special security sandbox. The security manager ensures that the applet does not step out of the sandbox. This means that applets are not normally allowed to access anything on the local machine (the machine on which your browser is running).
The applets that you access on this site do step out of the sandbox. This is allowed only under an agreement between us (the developers of the applet) and you (the client). You will be prompted to see if you are willing to accept our signed certificate. This certificate is an authentication that we (the developers) really are who we say. The certificate is authenticated by Thawte.
If you are using a NetScape browser, then you will first be asked if you accept the certificate which identifies us. Each time that the applet attempts to access your machine (either to print or read a file), you will be prompted if you are willing to allow the applet to do so.
If you are using an Internet Explorer browser, then you will be asked if you accept the certificate. Accepting the certificate implies your agreement to allow the applet to access your machine.