Can a applet be written to be malicious to a network?

So the way and applet that can enhance network security is that the applet can only run as it is told to run. Not accessing files, read or write access, etc. Can a applet be written to be malicious to a network? Does the core issue depend on who wrote the code?

An applet file that prompts the user for an ID number and an age.

I need to write an applet file that prompts the user for an ID number and an age. Create an Exception class and throw an Exception of that class if the ID is not in the range of valid ID numbers (zero through 899), or if the age is not in the range of valid ages (0 through 89). Catch the Exception and then display an appropriate message. Save the program as BadIDAndAge.java

I need the comments added throughout the BadIDAndAgePanel.Java + HTML file

I need the HTML file For the BadIDAndAgePanel.Java I need the comments to be added through out the code. This is an applet so I need the HTML file as well. This is the overall objective it must meet these minimal amount of instructions. Write an applet that prompts the user for an ID number and an age. Create an Exception class and throw an Exception of that class if the ID is not in the range of valid ID numbers (zero through 899), or if the age is not in the range of valid ages (0 through 89). Catch the Exception and then display an appropriate message. Save the program as BadIDAndAge.java

Java program for mail-order company

I need a program for a mail-order company. The program uses a data-entry screen in which the user types an item number and a quantity. Write each record to a file. Save the program as MailOrderWrite.java Write another program that reads the data file created by the MailOrderWrite program and displays one record at a time on the screen. Save the program as MailOrderRead.java I need the HTML file as well as comments added through out the code as well.

Data Model

Draft a simple data model that outlines a database management system. This model needs to track people's participation in various fitness activities at a fitness center. List at least 3 entities and at least attributes for each entity.