Do not copy other people's files and present them as your own. Plagiarism is plagiarism, whether it occurs electronically or manually. It is illegal to use copyrighted software unless you have purchased a copy. Yes, the price of software is high, and yes, it is often easy to copy. But that does not make it ethical or legal to do so.
Programmers make their living by the programs they sell.
If you cannot afford a program, don't use it. Most of the software you will need to do academic work is available for your use over the network or in public labs. If you are unsure whether a piece of software can be copied freely or whether it is copyrighted, please ask the Academic Computing staff. Curb the spread of viruses. Viruses are a fact of life wherever there are computers being shared by many people.