Start the appletviewer with more than one applet running and then hit
the quit box (the box in the upper right with the X in it) on one of
the windows. The application will freeze and you must use Ctrl-C to
exit.

The description field as copied from bug report 1225579 follows:

When you open an html document with multiple applet tags or when you clone a single
appletviewer window, you cannot close the appletviewer without resorting to using the
End Task dialog box in Windows.

Steps to reproduce:
cd \\java\\demo\\MoleculeViewer
appletviewer example3.html
// after the applet viewer opens the four molecule windows
Close a window

WORKAROUND:
WinNT: Bring up task manager, end Appletviewer task
Win95: Press <Ctrl+Alt+Del>, end Appletviewer task