Internet and system security explained
This article discusses the differences between viruses, trojans, spyware, adware, hackers and crackers.
Virus
A virus is computer program that has the ability to copy itself and therefore needs to be attached to an executable file. They often attach themselves to legitimate programs which increases their chance of being triggered. It can spread from PC to PC via removable media such as USB drives, CD/DVDs and over a network. There are two main types, resident and non-resident. Resident viruses load themselves into memory and start when the operating system executes a file. Non-resident viruses instead search for other hosts to infect and then replicate. It is important to always have an up-to-date antivirus program on your machine. Once your machine is infected it might prevent antivirus software from loading or blocking access to the update servers. If you are affected the first thing you can do is run a free online scan from Trend Micro or ESET. In terms of prevention Comodo Internet Security Personal is an excellent package where you can choose to install just the antivirus and firewall components or the full suite. If you're looking for just an antivirus then Avast or Avira are very good.
Trojan
A Trojan is something that appears to be a useful program but it brings with it undesirable software that open your system up to attack and harm the system. Unlike viruses, Trojans do not replicate but instead open up doors for hackers and viruses to get in. Your PC can come under attack in a number of ways - your personal data can be compromised, system crashes occurring, modification and deletion of files and your computer can be used as part of a larger attack against another computer. In terms of removal and prevention please refer to the tools in the antivirus section.
Adware
Adware is a type of Trojan where a piece of software (or a website) masquerades as something useful by telling you that your system is infected and offers a "free" solution to help you remove it. Once you accept the malware installs itself and can cause any number of problems to your computer. If your computer is behaving in a strange manner and you are seeing unwanted popups or your home page is being changed by itself your machine might be infected. To scan and remove this type of threat for free you can download Spybot Search and Destroy from Safer Networking.
Spyware
Spyware is malware that is secretly installed on your computer. It monitors the usage of the computer and can track your browsing history, install additional software, hijack your browser and even record keyboard input. Its profile is somewhat similar to that of adware and the detection and removal methods are the same.
Hackers
Hacker is the title normally associated with someone who gains unauthorised access to a system, however the correct term for this type of person is a "cracker". The strict definition of a hacker is "a person who delights in having an intimate understanding of the internal workings of a system, computers and computer networks in particular" [1]. A hacker is a clever programmer who has a keen interest in a programming language, enjoys the process of programming rather than just the theory, is able to appreciate the work of other hackers and picks up programming quickly.
Crackers
Crackers are those who breach security measures to gain access to a computer or computer network. The reasons for doing so vary greatly and can include gaining access to confidential information, modifying or deleting electronic information or rendering a system unusable. Crackers may engage in this behaviour for profit, for some cause (consider the group Anonymous taking out threats against Wikileaks), or because it's a challenge. The chance of a hacker directly targeting your average home PC is quite low as they will only go after high value targets such as servers.