One of the common blunders I used to make was getting confused between ‘viruses’,’trojans’ and ‘worms’ and use these terms interchangeably as if they are the same. So decided to look it up and get it clear. I know its just the basics and most of you people must be knowing it. Just for the ignorant here’s a note on that.
A computer virus attaches itself to a program and starts it’s journey. Mostly it comes along with an exe file(geeks out there..stop laughing:-P), means the virus may exist on your pc ,but wont infect it unless you run the file. ie, a virus cant be spread without a human action. Some of the main types of viruses are,
Boot sector infectors, which attacks the vulnerable boot program (which starts loading the operating system) which would be on the hard disk or bootable floppy disk or something. As we know the boot program is executed on start up which makes it a juicy target for virus writers…coz it is guaranteed the their code will be executed ,giving them full control of the system. Mostly these viruses are spread through infected bootable floppy disks.
File infectors, which modifies the program files, usually .exe or .com files and when the file is run, the virus executes and does whatever it was supposed to. These are spread through infected disks as well as through the net.
Macro viruses, which make use of the built-in programming languages in popular programs like Microsoft Word and Excel- which allow users to create programs that automate tasks, called macros. The virus writer writes malicious macros, which when opened unknowingly would spread like a regular virus. The regular viruses are written on low level machine language programs whereas the macro viruses are high level interpreted BASIC programs!
Trojans(people write from their own experience in tech blogs which is better than merely copy pasting…here’s something finally which I have had some experience at..sighhhh!)
,these are something which at your first glance will appear useful while in actual it may create a havoc!(yeah…my 40 GB HDD gone down the drain..thank god that the guarantee period wasn’t over). Those receiving Trojans are actually tricked into opening them because they appear to be receiving legitimate software or files from a legitimate source(ironic that I got it while I was installing antivirus). Trojans may create backdoor on your pc, but unlike worms and viruses it donot reproduce by infecting other files or self replicate.
Worms are a subcategory of viruses actually, but unlike a virus, it has the capability to travel without any help from a person. The biggest danger with it is that it replicates itself on the system thus it could send out hundreds or thousands of copies of itself, like sending itself to everyone listed in the e-mail address book. Due to the copying nature of the worm, it takes much system memory causing web servers or the computer itself to stop responding. Some of the popular worms are Mydoom, ILOVEYOU http://en.wikipedia.org/wiki/ILOVEYOU etc.I know this was boring, but hope atleast some were enlightened or got a clearer picture.

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