Originally posted by Stephanie Grasson:
The reason for making a trusted applet is to give the applet more permissions than it would usually have.
For example, applets normally cannot read or write files on the client's machine. This is a good security measure. The user feels confident that they can use the applet without any bad consequences to their system.
Perhaps your applet needs to write a file on the user's system. You must get special permission from the user to do so. First, the programmer makes a trusted applet by digitally signing it. This is done so that the user can verify the signature and feel confidant that they trust the applet's creator not to damage their system.
For detailed information about signing applets, see here: http://developer.java.sun.com/developer/onlineTraining/Security/Fundament als/Security.html#secSigning
Once the client has verified the signature and granted permission, your applet can proceed.
Generally speaking, you should not let your applet "out of the sandbox" (giving it more than normal permission) unless absolutely necessary.
Hope this helps.