Computer Worms, Computer Viruses and Trojans have one similarity. They all are malware.
What is a malware ?
Malware is an abbreviated form of Malicious Software. It indicates any software which is used for malicious purposes like stealing private data, corrupting files, crashing hard disks, extorting money etc. They infect a computer stealthily, without the user’s knowledge. And then spread themselves.
But, there are subtle differences among all these terms, though their intention is similar. So, what all are the differences among them ?
Let’s start by Computer Worms.
Computer Worms are malware which infect a computer without the user’s knowledge, like other malware do. And then it spreads through self-replication.
But unlike Computer Virus, they do not need to attach themselves to an existing program. It often uses computer networks and spread itself taking the advantage of security vulnerability of an existing software.
They almost always cause some harm to the network, by taking lots of bandwidth if not anything else. And after infecting a computer, they can delete files, use the computer as a botnet and use its computer resources for illegal activities, send spams or even blackmail companies by threatening about DoS or Denial of Service Attacks.
Computer Viruses also infect a computer and then spread themselves to infect more computers. They normally attach themselves with other computer programs, so that, when a user executes the program in his computer, they infect the computer. Just to give a common example, Microsoft Word Document support macro so that it can execute while opening the document. A virus can attach itself to a Word Document as a macro, so that, whenever a user will open the document, the code of the virus will be executed and the computer will be infected.
Computer Viruses can attach themselves to data files also. For example, a virus can attach its code to a jpg file and change the name of the file to jpg.exe, so that, whenever a user will open the file, unknowingly his computer will get infected.
A virus can affect the Master Boot Record or MBR of a computer also. And when that happens, it can survive through reinstallation of Operating Systems.
Computer Viruses can perform many harmful activities like corrupting hard disks, deleting files, degrading performance of computer, display unrelated messages on computer screen, stealing private data by logging keystrokes, spamming contacts etc.
The word Trojan is derived from the ancient Greek wooden horse that the Greeks used to invade Troy stealthily. Trojan programs generally tricks a user by some form of social engineering and get loaded and executed into the system. They often misrepresent themselves to appear useful, routine or interesting to the user and persuades the user to install it.
Trojans can infect a computer by clicking on a suspicious link, opening email attachment or even by installing software from untrusted sources. Sometimes, they even misrepresent themselves in unsafe websites as Anti-Virus software and when a user installs them, they infect the computer.
But unlike, Computer Worms and Computer Viruses, they do not self-replicate themselves.
Spyware and Ransomware are types of Trojans. Spyware infect a computer to steal sensitive private data or spy on the activities of the user. And Ransomware also do the same, but for blackmailing the user to extort money.
Trojans, when they infect a computer with elevated privileges, can do much harm. They too can corrupt hard disks, corrupt data, crash a computer, format disks, infect MBR or Master Boot Record of a computer and they can even steal sensitive private data or encrypt user files to extort money.
Computer Worms, Computer Viruses and Trojans have similar prevention techniques.
Do not click on suspicious links.
Do not open suspicious email attachments.
Install software from trusted sources only.
Update recent patches of software immediately.
Keep your computer updated with a trusted security program.
Do nor pay money if someone is trying to extort money by infecting your computer.