Just as you would not try to break into someone else's room, you should not try to log into anyone else's account or read their electronic mail. Other people's files are their own personal property. A person's files are his or her own personal property, whether they are on a floppy disk, a hard drive, a Macintosh server, or a UNIX system. Just because the person may have left his or her files where others can access them does not mean that others are welcome to open and read them. 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.