What are files with a .jar extension?

The icon with a JAR file extension indicates a Java application that can be started with a double click.

The file extension .jar identifies Java Script archives that have been packed with ZIP compression. In addition to graphics, videos and audio files, these archives can of course also contain executable Javascript files.

The icon with a JAR file extension indicates a Java application that can be started with a double click.

The icon with a JAR file extension indicates a Java application that can be started with a double click.

These jar files can be opened on both Mac and PC with a simple double-click. The Java Runtime (JRE) required to run the Javascript applications is already preinstalled on most computers, but can also be used here for all platforms such as macOS, Windows and Linux java.com can be downloaded for free. Incidentally, the Java.com domain belongs to the company Oracle.

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A warning: viruses hide in jar attachments

The advantage that Java Script offers - namely that it runs relatively platform-independently - is also appreciated by hackers and malware programmers. For this reason, viruses are not infrequently received in emails with an attachment that has a .jar file name. These attachments should not be clicked on under any circumstances, as they start with a double click and may attack the system in this way.

You should also exercise caution if you have downloaded the jar file from the Internet or received it from unknown persons. It is not uncommon for malware to hide behind these files, which then lodges itself in various parts of the computer and spies on the user, takes over the computer as part of a botnet or damages the system.

With a Javascript obfuscator scripts can be made illegible for humans in order to hide the content.

With a Javascript obfuscator scripts can be made illegible for humans in order to hide the content.

Unzip and view jar files

If you are familiar with Java Script, you can decompress any .jar file with an unpacker for Windows or macOS and then look at the source code or the content of the archive.

In many cases, however, the code will be made illegible by a Javascript obfuscator. These programs rename variables into cryptic names and, by removing line paragraphs, comments and similar aids, ensure that a person has great problems reading and understanding the source code.

Would you like to find out more about other file extensions? Then have a look at my articles .aae, .doc, .rar, .thm, .lrv or .nib Files over.

 

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