What is a computer virus?
A computer virus is a piece of malicious code that is designed to replicate itself and spread from computer to computer. A virus will typically attach itself to a file or piece of software and then wait for someone to execute the file or program. Once the file or program is executed, the virus will then infect other files on the computer and then attempt to spread to other computers.
A virus will typically cause some kind of harm to the infected computer, such as deleting files, corrupting data, or displaying unwanted advertising. Some viruses are designed simply to cause mischief, while others can be much more destructive.
There are many ways that a virus can spread, including email attachments, infected websites, and USB drives. It is important to be careful when opening email attachments and only visit websites that you trust. If you think your computer has been infected with a virus, it is important to run a virus scan as soon as possible to remove the virus and prevent it from spreading..Citation
The most dangerous computer virus of all time
Over the last few decades, computer viruses have become increasingly sophisticated and widespread, with some wreaking havoc on a global scale. Here we take a look at the 10 most dangerous viruses of all time.
1. ILOVEYOU
Also known as Love Letter or Lovebug, this computer virus caused estimated damage of $5.5 billion after infecting 50 million computers in just 10 days in 2000. The virus was spread via email, with users tricked into opening attachments containing the malware. Once opened, the virus replicated itself and sent itself out to everyone in the victim’s address book. As well as causing a massive amount of financial damage, ILOVEYOU also resulted in many businesses shutting down due to the sheer volume of emails it generated.
2. Code Red
First appearing in 2001, the Code Red virus infected over 359,000 systems within 14 hours, ultimately causing an estimated $2 billion in damage. The worm took advantage of a buffer overflow vulnerability in Microsoft’s IIS web server software, allowing it to gain control of systems running the affected software. Once infected, the worm would scan for other systems to infect and would deface any web pages hosted on the server. Code Red was particularly noteworthy as it was one of the first worms to spread via the internet without any user intervention.
3. Slammer
Slammer was a fast-spreading worm that surfaced in January 2003, infecting over 75,000 systems within 10 minutes. The worm took advantage of a buffer overflow vulnerability in Microsoft SQL Server and caused a Denial of Service (DoS) attack on systems it infected. The worm was notable for its speed of propagation, which was made possible by the fact that it didn’t need any user intervention to spread. The Slammer worm caused an estimated $1 billion in damage and was responsible for taking down major sites such as CNN, Bank of America, and Microsoft.
4. Sasser
Sasser was a worm that first appeared in 2004 and quickly spread to infect over half a million systems. Like Slammer, Sasser took advantage of a buffer overflow vulnerability in Microsoft software, this time in the Local Security Authority Subsystem Service (LSASS). The worm would cause infected systems to crash and then reboot, resulting in a Denial of Service (DoS) attack. Sasser was notable for the fact that it could spread without any user intervention, making it particularly difficult to defend against.
5. MyDoom
MyDoom was a worm that first appeared in 2004 and quickly became the fastest-spreading email virus of all time. The worm was spread via email attachments and would replicate itself once opened. It would also disable security software on infected systems and open a backdoor that could be used by the worm’s creator to remotely control the system. MyDoom caused an estimated $38 billion in damage and was responsible for taking down major sites such as Google, Yahoo, and Microsoft.
6. SoBig
SoBig was a virus that first appeared in 2003 and quickly became one of the most widespread viruses of all time. The virus was spread via email attachments and would replicate itself once opened. It would also disable security software on infected systems and open a backdoor that could be used by the worm’s creator to remotely control the system. SoBig caused an estimated $37.1 billion in damage and was responsible for taking down major sites such as Google, Yahoo, and Microsoft.
7. Conficker
Conficker was a worm that first appeared in 2008 and quickly became one of the most widespread viruses of all time. The worm was spread via email attachments and would replicate itself once opened. It would also disable security software on infected systems and open a backdoor that could be used by the worm’s creator to remotely control the system. Conficker caused an estimated $9.1 billion in damage and was responsible for taking down major sites such as Google, Yahoo, and Microsoft.
8. WannaCry
WannaCry was a ransomware worm that first appeared in 2017 and quickly spread to infect over 230,000 systems in 150 countries. The worm took advantage of a vulnerability in Microsoft Windows that allowed it to gain access to systems and encrypt files. Once infected, victims were instructed to pay a ransom in order to regain access to their files. WannaCry was notable for the amount of damage it caused, with an estimated $4 billion in damage.
9. NotPetya
NotPetya was a ransomware worm that first appeared in 2017 and quickly spread to infect over 10,000 systems in 64 countries. The worm took advantage of a vulnerability in Microsoft Windows that allowed it to gain access to systems and encrypt files. Once infected, victims were instructed to pay a ransom in order to regain access to their files. NotPetya was notable for the amount of damage it caused, with an estimated $1 billion in damage.
10. Stuxnet
Stuxnet was a computer worm that was discovered in 2010. The worm was designed to targeted industrial control systems, specifically those used in Iran’s nuclear facilities. The worm was able to spread via USB sticks and would infect systems, causing them to malfunction. Stuxnet was notable for being the first piece of malware that was designed to physically damage equipment. The worm is believed to have caused significant damage to Iran’s nuclear program and set back their efforts by several years.
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