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Top 10 Computer Viruses


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Creeper was possibly the very first computer virus, although this is contested. It was invented back in 1971 by Bob Thomas, using the Tenex operating system, and used the precursor of the internet, ARPANET, to spread between DEC PDP 10 systems.

Creeper did nothing more than display the message "I'm the creeper, catch me if you can!" It was an example of a simpler age. (Indeed, Creeper's creator also released a cleaning program called "Reaper" that removed the Creeper code. This was the first anti-virus virus program.)



Brain was the first virus written for Microsoft's DOS operating system, back in the mid 1980s. It was originally developed to stop the copying of a medical software program developed by two Pakistani brothers, Basit and Amjad Farooq Alvi.

Brain spread by floppy disc and copied itself into the boot sector of the media. It displayed the names of the creators and suggested the infected recipients got in contact to get disinfected. It spread quickly and the two brothers were inundated with calls from people around the world demanding that their machines were disinfected. Such was the volume of calls that the two eventually had their phone lines cut off.


Elk Cloner was written by a 15 year old high school student called Rich Skrenta as a practical joke. Unfortunately for him the joke turned bad very quickly. The virus was developed for the Apple II system and was a boot sector virus that spread via floppy discs (mostly through pirated games). Skrenta devised a way to alter discs automatically and the Elk Cloner virus was invented.

It had little in the way of a payload. Every fiftieth time a person booted an infected disc the software ran a little program on the computer screen, and that was it. Nevertheless it was a serious annoyance and was a harbinger of things to come.



The late 90s-early 2000s were not only the golden age of the internet, they also seemed to be the golden age for malware. Over that time period, few viruses were able to match the reign of Klez. Like many other viruses of its time, Klez spread through email. Users were duped into opening infected files and, once the malware was installed, the victim's address book was opened and copies of the attack were sent to contacts.

Klez, however, took this a step further. Not only did the virus send itself to people in your address book, it also pretended to be from other people. Later, the worm wreaked further havoc by pretending to be its own removal tool. Klez is a cunning little devil, and variants are still doing the rounds today.



ExploreZip was written over a decade ago but can still be found in the wild today. ExploreZip, like most viruses of the time, targeted Windows systems and was spread via email. The recipient got an email reading “I have received your email and I shall send you a reply ASAP. Till then take a look at the attached zipped docs.”

Clicking on the attachment booted the virus onto the user's computer and it immediately spammed itself out to all of the contacts in Outlook. More worryingly it also overwrote Word documents with lines of zeros and did some damage to the operating systems itself. As destructive worms go it wasn't too bad, but in the pre-Millennium days of 1999 it certainly caused a panic.



When a New Jersey hacker wrote a small bit of code he named after a stripper he met in Florida, he had no idea the chaos that would ensue. The virus spread like wildfire throughout the net, and an unintended effect of the worm led to a glut of email traffic that overflowed servers and caused tons of damage and lost work time to corporate IT systems.

The real damage of Melissa was not in the code itself, but in its spamming capabilities. Current computer malware writers have taken note of code like Melissa and now fly much lower under the wire to attract less attention. The hacker himself was later caught and sentenced to a year and half in prison. Next time he wants to impress a girl, hopefully he'll stick to chocolates and jewelery.



A week after the September 11th atrocities a new virus hit the internet in a big way. Nimda was one of the fastest propagating viruses in history, going from nowhere to become the most common virus online in 22 minutes according to some reports. The reason for this speed was that Nimda used every trick in the book to spread itself. It used email, open network shares, used IIS vulnerabilities and even used web sites to spread. It hit pretty much every version of Windows available and appeared all over the place.

Nimda struck at a time when everyone was on edge and all types of threats were given plenty of media coverage. This, in part, helps to explain why the Nimda worm got the attention it did.



MyDoom was interesting because it was one of the first to use peer to peer as a transmission device. The worm not only spread itself through email address books but also through the shared folder of users who ran the Kazaa file sharing application. In other words, it took full advantage of people downloading files onto their computers from an untrusted source.

While definitely skilled programmers, MyDoom's creators also seemed to be fans of good old-fashioned vigilante justice. One of the early tasks performed by infected users was to take part in a denial of service attack against SCO, the infamous software vendor that once tried to lay claim to the patents for Linux.



Before Conficker came around and got everyone worked into a lather, Storm was the big bad botnet on the block. First appearing in early 2007 as a fake news video on European flooding, the Storm malware menaced users for more than a year. The malware disguised itself as everything from video files to greeting cards, and attacks were continuously refreshed to coincide with holidays and current news event stories.

At a time when many were seriously concerned about the health and safety of friends and family the last thing anyone needed was an infection. While Storm has since been eclipsed by newer botnets, the name still brings to mind one of the most menacing attacks seen in recent years.



The third form of the Conficker attack provided nice theatrics, but little in the way of actual damage. The premise was simple: Conficker.C would spread to as many machines as possible throughout March 2009. Each infected machine was given a huge list of domains, one of which would be contacted by 1 April. The deadline made all the difference. Now, Conficker wasn't just a simple malware infection, it was a "Ticking Time Bomb". The botnet remains intact and still poses a threat, but nothing near the cyber-carnage that many spoke of.

The media panic over Conficker has shown that people are still scared of viruses. It had a funny sounding name, was mysterious and was set to do something on a 'magic' date : in other words, it hit all the right buttons.

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Cool post. I've been lucky enough to never have gotten a computer virus in all the years I've owned any of my own computers. Knock on wood...don't want to jinx myself.

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Cool post. I've been lucky enough to never have gotten a computer virus in all the years I've owned any of my own computers. Knock on wood...don't want to jinx myself.

A lot of times it can be undetected, I have used my pc as a honeypot many of times and just had it pumped full of hackers and virii for the fun lol then I can look and see how they are attacking my pc. Very good post man.

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I knew you guys were gonna like it, but they missed out a few ones too.

I love you and Bug Bear

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