For years we've called anything that attacks our computer a virus. And in the early years of computing, they were. However, nowadays we are seeing many varied types of infections. Because of this the industry has broken them into categories based on behavior. So, let's take a look at some of the more common infections as defined by Wikipedia. Virus - A computer virus is a computer program that can replicate itself and spread from one computer to another. Malware - Short for malicious (or malevolent) software, is software used or created by attackers to disrupt computer operation, gather sensitive information, or gain access to private computer systems. Adware - Any software package which automatically renders advertisements in order to generate revenue for its author. The advertisements may be in the user interface of the software or on a screen presented to the user during the installation process. Trojan - A type of malware which appears to perform a desirable function but instead gains unauthorized access to the computer system. Trojans do not attempt to inject themselves into other files like a computer virus. Trojan horses may steal information, or harm their host's computer systems. Ransomware - We are seeing a lot of this type. It is a class of malware which restricts access to the computer system that it infects, and demands a ransom paid to the creator of the malware in order for the restriction to be removed. Examples are fake FBI and Department of Justice infections. Worm - A standalone malware computer program that replicates itself in order to spread to other computers. Often, it uses a computer network to spread itself. Rootkit - A rootkit is a stealthy type of software, often malicious, designed to hide the existence of certain processes or programs from normal methods of detection and enable continued privileged access to a computer.