Computer viruses pose a major threat to the software industry. The document outlines what computer viruses are, their types including Trojan horses, worms, and macros. It discusses why people create computer viruses such as for profit, threats, or as a hobby. It also describes how viruses can enter systems like through the internet, flash drives, or disks and warns signs of infection like sluggish performance or crashing. The document concludes by providing virus prevention guidelines including using antivirus software, regular scanning, and backups.