A signed applet has a certificate with a digital signature that confirms it originated from a trusted server. When a Java plug-in encounters a signed applet, the plug-in checks the certificate to ensure that the applet was created and signed by the individual who made the certificate. The plug-in also verifies that the contents of the Java applet haven’t been modified or tampered with.
You can choose from these security options:
Trust: You trust the author of the applet and want to run it.
Don’t Trust: You don’t trust the author of the applet and don’t want to run it.
Show Certificate: Lets you examine the attributes of each certificate in the certificate chain. If you want to always trust the author of the applet, click Show Certificate, then select “Always trust these certificates.”