If the Extension installer is not signed, there should be a security warning.
However, the installer program is running without a warning message.

http://comanche.eng.sun.com/jawstest/extensionInstaller/IM_ExtInstall_NotSigned.jnlp


After installer program exit (even if I sign the installer program), there is
an other exception message:

General Message:

An error occurred while launching/running the application.

Title: Java Web Start Test Case -- Extension Installer
Vendor: Sun Microsystems, Inc.
Category: Security Error

access denied (java.util.PropertyPermission user.home read)

Exception Message:

java.security.AccessControlException: access denied (java.util.PropertyPermission user.home read)
        at java.security.AccessControlContext.checkPermission(Unknown Source)
        at java.security.AccessController.checkPermission(Unknown Source)
        at java.lang.SecurityManager.checkPermission(Unknown Source)
        at java.lang.SecurityManager.checkPropertyAccess(Unknown Source)
        at java.lang.System.getProperty(Unknown Source)
        at com.sun.javaws.ConfigProperties.getSystemProperty(ConfigProperties.java:132)
        at com.sun.javaws.ConfigProperties.getConfigFilePath(ConfigProperties.java:140)
        at com.sun.javaws.ConfigProperties.store(ConfigProperties.java:808)
        at com.sun.jnlp.ExtensionInstallerServiceImpl.installSucceeded(ExtensionInstallerServiceImpl.java:125)
        at ExtInstaller.install(ExtInstaller.java:22)
        at ExtInstaller.main(ExtInstaller.java:32)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.sun.javaws.Launcher.executeApplication(Launcher.java:687)
        at com.sun.javaws.Launcher.executeMainClass(Launcher.java:650)
        at com.sun.javaws.Launcher.continueLaunch(Launcher.java:533)
        at com.sun.javaws.Launcher.handleApplicationDesc(Launcher.java:327)
        at com.sun.javaws.Launcher.handleLaunchFile(Launcher.java:154)
        at com.sun.javaws.Launcher.<init>(Launcher.java:113)
        at com.sun.javaws.Main.main(Main.java:149)