Computer viruses are malicious software programs that infiltrate systems to disrupt operations, steal data, or cause damage. They can replicate and spread across networks, causing widespread harm. There are various types of viruses, each with distinct characteristics and attack methods. Common types include file infectors, which attach themselves to executable files; macro viruses, which target documents and applications like Microsoft Word; boot sector viruses, which infect the master boot record of a computer; and polymorphic viruses, which constantly change their code to evade detection. Understanding the different types of viruses is crucial for implementing effective cybersecurity measures.