About Java applets
A Java applet is a small software program written in the Java programming language, a programming language used primarily on the World Wide Web. By adding a Java applet to a Web page, you can add special effects, interactivity, and more. For example, you might add an interactive game or a window for entering or viewing information on a Web server.
A Java applet is stored in a separate file that you can reference in a Web page. Although you cannot create a Java applet by using Microsoft FrontPage, you can use FrontPage to create or edit the HTML code that references a file for a Java applet.
If you open a Web page in Design view, and that page contains a reference to a Java applet, an icon representing the applet 
appears on the page. The icon does not appear when you open the Web page in a Web browser or when you print the Web page.
Although some Java applets are self-contained and work correctly in any location on a Web page, other Java applets are dependent on the structure of a page. If you copy or move such an applet to another Web page
Because some Web browsers provide settings for disabling or limiting the functionality of Java applets, an applet may or may not work correctly for all of your site visitors.
Important Security vulnerabilities in external files or controls may extend to Web pages that use those items. For example, external style sheets (files with a .css extension), script files (files with a .js extension), custom ASP.NET controls, or other items, may pose a security risk. Be sure your style sheets, add-ins, themes, executables, scripts, controls, or other files come from trusted sources.