Understanding Malicious Software and Other Security Threats

One unfortunate side effect of being constantly connected to the Internet is that our computers are always open to infection by malicious software and other security threats. While you can never expect to be one-hundred percent safe, a little vigilance combined with the latest in antimalware solutions make it highly unlikely that you will become a victim. What many novice computer users don’t realize is that there are actually many forms of malicious software ranging from the annoying yet fairly harmless to that which can practically change the course of a war. The following takes a look at the various types of malicious software and other security threats affecting computers around the world today.

Computer Viruses

Viruses are the best known type of malicious software, and they have been around since the beginning of computer software itself. Viruses are created to disrupt and damage often for no other reason than the programmer’s amusement. Computer viruses are not independent programs and are instead malicious lines of codes which connect themselves to programs and replicate themselves when an infected program is run. Some viruses do not even modify the size of the file that they infect, instead overwriting unused lines of code. One of the most devastating computer viruses was the CIH virus. After its appearance in 1998, it caused up to a billion dollars of damage across some 60 million computers by overwriting motherboard firmware rendering the hardware useless.

Computer Worm

Unlike viruses, computer worms are standalone programs. Like viruses, however, they also replicate themselves and spread themselves over networks to infect multiple computers. They take advantage of security flaws in order to achieve this. Worms are usually more of annoyance than a danger, since they do not modify data. Instead, they can cause disruption by using up network bandwidth and slowing down the connection as a result. Today, worms are rarely a problem thanks to increasing security measures and improved technology in networks and operating systems. The last major disruption caused by a computer worm was in 2008 when the Conficker worm infected millions of computers around the world. This was also one of the most harmful worms to ever appear, since it disabled antivirus software.

Trojan Horse

While there are plenty of legitimate programs such as remote desktop software which do much the same thing, a Trojan Horse exists solely for malicious purposes. Like remote desktop software, it allows someone to access and control a computer remotely. However, a Trojan typically ends up on a computer without the owner’s knowledge, allowing the remote hacker to gain access. A Trojan consists of two parts – the client component on the victim’s computer and the server component on the hacker’s computer. Trojans are among the most dangerous among malicious software since they leave your computer completely at the mercy of the hacker who may steal any personal or financial information you have stored on the computer or decide to delete or damage your files.


Spyware is software, or a component of a program, designed to collect data about things such as your browsing habits. Spyware does this without your knowledge or permission and then uses this data for advertising purposes or to sell on. Spyware is often unwittingly installed by users who fall for the tactics that malicious websites use to encourage people to download it. Sometimes known as ‘scareware,’ spyware may first appear in the form of a popup window in a browser telling you that your computer is vulnerable or that your browser is out of date in an attempt to scare you into installing the program as a solution. Some spyware may hijack your browser as well by constantly taking you to a malicious website instead of your homepage. Spyware is often notoriously difficult to remove.


The keylogger is the ultimate too for any cyber-thief as well as the most harmful type of security threat out there. Keyloggers work similarly to Trojans in that they consist of a client and a server. The client ends up on your computer, typically without your knowledge. The client then monitors every single keystroke and sends this information to the hacker’s computer. This allows them to read absolutely everything typed on the remote computer such as passwords, emails, chat messages and Web addresses. For obvious reasons, this has the potential to lead to a security disaster. That being said, there are also commercially available keyloggers designed for monitoring staff, children or spouses, although whether they can really be used for ethical purposes is certainly questionable.


Rootkits are not always malicious, but ones which are can allow a hacker to have access to your computer to an extent. Rootkit installations are typically automated, further opening the path for the installation of additional malicious software. Rootkits typically work by exploiting security flaws in user privileges and group access management. There have been a number of high-profile cases involving rootkits such as the Sony BMG rootkit scandal which used rootkits installed without users’ permission in an aggressive attempt to combat music piracy. Another case in which rootkits were extensively used was the Greek wiretapping case in 2004 when some 100 phones belonging to Greek government employees were hacked into and monitored.


Phishing is not a type of malicious software itself but rather a common tactic used to dupe people into giving away personal and financial information to criminals. Phishing refers to the acquisition of sensitive information such as credit card details or passwords by masquerading as a legitimate online service. Phishing attempts often appear through spam email or fake websites which pretend to belong to a well-known company. For example, if you make a mistake when typing in a web address, you may sometimes end up on a fake version of the real website and unwittingly enter a password or some other sensitive information. Unsurprisingly, phishing can lead to disastrous consequences. Fortunately, however, it is getting rarer as browsers and security companies crack down on it heavily.


Adware is not really a form of malicious software in most cases, but it is mentioned here due to the fact that it is commonly misunderstood. Some free software uses integrated advertisements to support its development. These advertisements may appear in the form of banners in the program’s interface or as occasional popups. Advertisements might be annoying and sometimes intrusive, but they are also a perfectly legitimate way to provide financial support for software development. Where adware becomes malicious software is when advertising programs and spyware are installed on your computer without your knowledge. Some programs, such as the infamous Zango (now defunct), were often considered to be something between spyware and adware.