Web browsers nowadays possess enhanced security to prevent infections from computer viruses.

The applets are small applications (programs), written in Java. These programs are installed on servers and they are embedded in the HTML code comprising a web page. When the client computer downloads a webpage with an embedded applet ("carrier webpage"), then the user can execute it by clicking the relevant control buttons on the applet panel.

The "Java machine", which must normally be already installed on the client computer, undertakes the task of running the applet. When the user terminates the execution of the applet and/or leaves the web page, the applet is self-terminated and its code is discarded.

Until a few years ago, the aforementioned process was free and without any restriction or security measure, since the Java codes, that make up the applet, had no commands that could harm the client computer. However, as an additional security measure provided by the newer versions of the "Java machine" installed in each computer, it is no longer possible to run these applets, unless the user first declares explicitly to the "Java machine" that the website offering the applet is trustworthy. Then and only then, the "Java machine" will start running the applet.


Java Activation / Statement of Trust

General instructions for the whole process can be found in Oracle's webpages, the company that owns the Java software and updates regularly the computers on the Internet with the newer versions of it. This site is the following: http://www.java.com/en/download/help/win_controlpanel.xml.

From the same site, you can also download the latest "Java machine" and activate it. This usually happens only once: when you set up a new computer.

The procedure required for:

(a) Automatic update for newer versions of Java and

(b) Statement of Trust for selected sites,

is simple and the user can perform it with the following easy steps:

First we call our Java Control Panel as follows:

We select: from <Start Button> <All Programs> <Java> <Configure Java>, as shown in the following figures:

Search and find the "Configure Java" panel in Windows XP and Windows 7.

Search and find the "Configure Java" panel in Windows 10.


The following Java Control Panel appears. Note that from now and on, there are no significant differences with the different versions of Windows, since all panels and messages displayed are generated by the "Java machine" and not by Windows:

In this panel, click on the <Update> tab and the following panel appears, where we check the box "Check for Updates Automatically" and we select "Before downloading" in the "Notify Me" editbox.

By this, we instruct our computer to update its Java machine automatically after asking us, if we want to do so at this moment or at some other opportunity, using the same panel and clicking <Update Now>. After clicking <OK> the panel must appear as follows:



Then, we click on the <Security> tab, and the following panel appears:

There, we set:

(a) Select Security Level: High.

(b) In the "Exception Site List" we declare explicitly the sites we trust and we wish our computer to run the applets they send. For this declaration, click on the <Edit Site List> button, so the Editbox "Location" is displayed:

In the Editbox we type the site (by clicking the <Add> button we can declare additional sites, if so needed).


Here we type the following site: (this is the old server of the Department of Chemistry, which, presently, contains the applet pages).

It is recommended to add the following two sites, where the applet web pages are to be transferred (in one or the other) so it will be not necessary in the future to repeat the same task:

http://users.uoa.gr           http://www.chem.uoa.gr

Attention: we must type the sites correctly as shown in the picture (you can copy / paste from this site). After clicking <OK>, the frame with the Editbox should appear as above.

Now, our computer has been updated and is ready to "run" all applets received from the declared sites.


Running the Applet

As the last security measure, after loading of the webpage containing the applet, the following "security warning" appears:

Click the <Run> button and the applet starts running normally.

The list of educational applets installed on the Department of Chemistry server and their respective links are currently available at


IMPORTANT (Added on September 3, 2017)

Recent updates of the various browsers (Firefox, Chrome, etc.) do not make possible the execution of Java applets, since they do not have or do not support the Java Add On at all. However, there is still a way to overcome this problem by running their expanded versions or by internal calling of Internet Explorer, which still has the possibility to do so.

You can find the step-by-step instructions for each browser in the following webpage: "How to enable Java in all the major web browsers". By following these instructions, we were able to run our applets using the latest versions of Chrome and Firefox web browsers, in a Windows 10 environment.

Constantinos Efstathiou

(email: cefstath at chem.uoa.gr)

Professor Emeritus

Department of Chemistry, University of Athens

September 30, 2016