HD Doctor Blog

What is a computer virus and how do you get one?

If you depend on the information stored on your personal computer, you need to understand how computer viruses spread, and you should use anti-virus software to reduce the chance that a computer virus will infect your programs and files.

A computer virus is a program that makes copies of itself and infects files. Computer viruses can spread to other computers and files whenever infected files are exchanged. Often infected files come as email attachments, even from people you know. The email senders have no idea that they are passing on a file with a virus in it.

Some computer viruses can erase or change the information stored on your…

2. Sasser
Shaun Nichols: Just how much damage can a virus do? Well, take the Sasser worm as one example. This relatively simple little attack managed to cripple airlines, news agencies and even knocked out government systems.

Perhaps most frustrating, however, was that Sasser infection was very easy to prevent. The vulnerability which the attack exploited had been patched for months, and all users had to do was install the most recent security updates from Microsoft.
Sasser was a stark warning that has yet to be heard by many. Unpatched systems are still pervasive around the world, leaving users vulnerable to Sasser and countless other malware attacks that target patched vulnerabilities.

Iain Thomson: I remember the Sasser outbreak…

4. Nimda
Iain Thomson: A week after the 11 September 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, IIS vulnerabilities and even web sites to spread. It hit pretty much every version of Windows available and appeared all over the place.

In the paranoid days after the terrorist attack some speculated that this was a digital 11 September, and some security consultants got large speaking fees…

6. Storm
Shaun Nichols: 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 huge botnet was also influential for its continued use of social engineering tactics. The malware disguised itself as everything from video files to greeting cards, and attacks were continuously refreshed to coincide with holidays and current news events.

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.

Iain Thomson: When extreme weather hit Europe the…

8. Conficker
Shaun Nichols: The global catastrophe that wasn’t, the third form of the Conficker attack provided nice theatrics but little in the way of actual damage.

The premise was pretty simple: Conficker.C would spread to as many machines as possible throughout March. 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’, and a looming menace that would unleash carnage. Or at least that’s what the story turned into when unscrupulous security vendors and tech-newbie news outlets got hold of the story.

Then the deadline passed and, pretty much…

10. Elk Cloner
Iain Thomson: 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. Apparently Skrenta was a fan of pirated games and would swap them with his friends, sometimes with little messages added. After one too many of these infected discs, he devised a way to alter discs automatically and the Elk Cloner virus was invented.

It had little in the way of a payload. Every 50th time a person booted an infected disc the software ran a little program…

All this panic over a simple strain of flu got us thinking about some of the more virulent computer pandemics that have hit in recent years. While a computer virus pales in seriousness to a human outbreak, malware attacks can still take a huge toll on businesses throughout the world.

The viruses below may not have been the most widespread or effective, although many of them were. Instead they are the ones that stick in the mind as being particularly notable. There are been so many over the years, and viruses will always be a part of computing now, but these may bring back memories, not all of them pleasant.

Honourable mention: Creeper
Iain Thomson: Creeper was possibly the…