Along with a bag of goodies, the Internet brings with it a box full of viruses, spyware, and other malevolent programs. You've been warned too many times to always watch what you run on your PC. Or Mac. A malicious program, once run, can do anything, including send your confidential files over the Internet and mercilessly wipe your hard disk. If only all applications were written in Java, then you wouldn't need to worry so much.
Java was designed with security in mind and Java security was designed for:
Java users, i.e. people running Java applications. With Java, at least, there is ease of mind. However, as you will see later, Java users need to understand Java's security feature in order to configure security settings.