As computer professionals, our progress is strongly based on the contributions and prior art of others. We build new applications and tools on top of existing operating systems, libraries, and standards. Even when we start from scratch, we build on prior lessons learned about producing computer software and hardware. This type of borrowing is normal and even expected. Sometimes the use of the contributions of others goes way beyond borrowing to theft of work or plagiarism. This can range from the stereotypical boss who takes all the credit and none of the blame for his or her employees work and ideas to outright passing other people's work as your own. While the former is probably only unethical, the later is likely to be illegal. I've been seeing a lot of the later lately in our field and it's disheartening.
The really sad part about people passing off others' work as their own is that it is so unnecessary. I took a class recently where a distressingly high number of students plagiarized the writing assignment. Given the nature of the assignment, I honestly think that it would have taken more work to find appropriate content to steal than to actually write it. A recent scandal in the Information Security field involves an already poorly respected (but well-known) security professional who published a security book that turned out to be almost entirely copied from various websites (he blamed this on poorly supervised ghostwriters, but nonetheless, it was his name on the cover.) An anthology of the best of the web on each important security topic would probably have sold better (even had the plagiarism and/or ghostwriting not been discovered) and garnered as much or more fame and positive acclaim than actually writing yet another introductory computer security book while allowing the editor to build solid relationships with the contributors. I've caught people stealing my articles to use for web content and in most cases if they had asked I likely would have allowed them to use it and possibly even promoted their site. Plagiarism is getting easier and easier to detect, to the point where getting caught is becoming inevitable. And when you are caught, you lose more than you gained from stealing in the first place. If you cheat your way through school, you are only going to be stuck later when you can't actually produce in the work place.
As computer professionals, our reputation is extremely valuable. While there are some notable exceptions, having a reputation as being dishonest or committing illegal acts is likely to be very detrimental for your employability. Even if you find people willing to hire you, you may not be welcomed or accepted by your peers. From a purely pragmatic viewpoint, plagiarism is a stupid career move. More importantly, as computer professionals, we affect systems that people trust – with their innermost thoughts, their business data, even their life. It is up to us to live up to that trust by being personally and professionally trustworthy. If you are unable to do so, I recommend you find a different career.