Most people know the term malware, which is a generic term for any type of malicious software. But few people understand the different types of malware, so in the coming weeks we will provide a high- level description of the three main types of malware: virus, worm and trojan. We will start this week with virus.
A computer virus infects a legitimate application (e.g., Microsoft Word) in order to spread and reproduce itself. The virus isn’t a standalone program, but rather a snippet of code that inserts itself into a program. When that program is launched, the virus code is loaded into CPU memory and is now prepared to perform some nefarious activity.
The specific activity depends upon the intention of the person that created the virus. The virus might log keystrokes in order to capture passwords—this is a form of spyware. Or it could turn your computer into a zombie and use it to attack other computers (denial of service)—this is referred to as a bot attack. Or it could encrypt your data and demand payment to restore it—this is called ransomware. Or it might just destroy the host computer by infecting the operating system or erasing critical files. The type of destruction is almost limitless and left to the imagination of the bad actor that created the virus.
One final point to note is that infection by a virus requires some human action. In other words, a human user must download the virus in some way, for example via an email attachment or file from a website. Anti-virus programs are therefore designed to scan such files before they are downloaded to make sure they don’t contain a virus.