1. Computer Virus’s

2. So what is a virus?
A computer program that is loaded on your computer without your knowledge, with the intent of doing some damage to your system.
The effect of computer viruses varies from doing so little damage that you are unaware that your computer has been infected, to wiping out the entire contents of your hard disk.

3. So what does the virus do?
There are viruses which play music, display messages, change or delete files.
Computer viruses are manmade and most are intentionally designed to replicate themselves. When the virus program runs it makes a copy of itself and adds itself to another computer program. Each time the infected program is run, the virus is also run and in this way spreads. If your system is infected, you can easily spread the virus to others through shared disks and attachments

4. Trojan Horse
The term 'trojan horse' is used to describe a virus program that disguises itself as a benign application. Trojan horse viruses do not reproduce.

5. Worm
'Worms' are computer viruses that that are designed to copy themselves from one computer to another over a network.
Recent worm viruses have been designed to be spread via , e.g the 'love bug’

6. File Infectors
This is a block of code which attaches itself to another program and is able to copy itself into subsequent applications that you run.

7. Boot-Sector
Boot-sector viruses infect the area of the hard disk that are read and executed by the computer when it starts up.

8. Macro Viruses
Macros are small programs that can be used to carry out tedious repetitive tasks. For example, you can write a Word macro to add your name, address and phone number to documents. Macros run automatically when the file they are attached to is opened.
Macro viruses spread much more rapidly than other forms of viruses as people frequently share data files.

9. The Love Bug was a macro virus that caused considerable damage
The Love Bug was a macro virus that caused considerable damage. The subject of the was 'iloveyou' and had an attached file called 'love-letter-for-you.txt.vbs.'
The attachment was a Visual Basic macro that erased files on your computer. The virus then sent copies of itself to every address in the Microsoft Outlook address book. As these replicated messages spread they created jams in Internet traffic and the vast amount of mail caused Network servers to crash. It spread round the world in two hours affecting tens of millions of computers.

10. Your computer can become infected by a computer virus in a variety of ways:
From an infected floppy disk (or any other removable media e.g. Zip disks, CDs.)
By opening a file that is infected with a macro virus.
Through attachments infected with macro viruses.
From infected messages.
From hostile Java applets and ActiveX controls, you unknowingly download when browsing the Internet.
From infected programs downloaded from the Internet.

11. Some Recent Examples:

12. Sasser
The Sasser worm first appeared on 1 May and affects computers running Windows 2000 and XP.
This virus is called a “worm” because it can search out machines to infect by itself, without requiring any intervention from users—it does not spread by . It is very efficient at finding new computers to infect and it can cause networks to become congested and slow down.

13. A computer virus spread via has been described by security experts as the "largest virus outbreak in months".
The malicious worm, called Mydoom or Novarg, has clogged networks and may allow unauthorised access to computers.
It arrives as an attachment in a text file which sends itself out to other addresses if opened.
Security experts MessageLabs said, at its peak, one in 12 s carried the worm. It has now stopped more than 1.5 million copies of it.

14. Sven Jaschan
This year saw an upsurge in arrests of virus writers, most notably, the self-confessed author of the infamous NetSky and Sasser worms. The German teenager wrote his malware in a misguided attempt to remove spam-friendly viruses such as MyDoom from infected PCs. Instead he created a monster.
NetSky-P accounted for almost a quarter of virus incidents reported to Sophos, topping its annual chart. Five NetSky variants made it into Sophos’s top 10. So Sven Jaschan was responsible for more than 50 per cent of all virus incidents reported to Sophos in 2004.

15. Zafi-b
Security firms have issued warnings over a multilingual computer virus that can shut down firewalls and disable anti-virus software. Zafi-b, which is also known as Hazafi or Erkez-b, spreads both as an attachment and via peer-to-peer file-sharing systems, using techniques common to similar worms. The worm, first discovered last week and now spreading rapidly, is delivered in the form of a .pif, .exe or .com file.
Most interesting about the malware is its ability to speak in multiple tongues. Zafi replicates itself in Hungarian, German, Dutch, English, Italian, Swedish, Spanish, and Russian.