The Top 10 Most Destructive Viruses Affecting Computer Networks Worldwide

The Sasser virus first gained attention and began rapidly spreading on April 12, 2004. It was created by an IT student named Sven Jaschan. This computer worm is named 'Sasser' due to its method of spreading through a buffer overflow exploit. Sasser scanned various IP ranges and connected to victim computers via TCP port 445. The virus caused widespread disruptions, including the temporary shutdown of several French communications satellites (AFP), Delta Air Lines having to cancel numerous transatlantic flights due to computer systems being infected, Nordic insurance companies halting operations completely, and 130 companies being forced to close their offices. It also disabled electronic maps used by British coastguard patrols for hours, and X-ray machines at Lund University Hospital were rendered inoperable, requiring patients to be urgently transferred to nearby hospitals.

Ranked fifth is the Zeus virus, a Trojan horse malware that targets Microsoft Windows systems. It is primarily used to steal banking information or to install the CryptoLocker ransomware virus (a type of malware that demands a ransom; once it takes control of a computer, it encrypts critical files and demands payment to decrypt them. If the ransom is not paid, the files are permanently deleted). Zeus spreads mostly through downloads from compromised drives. It was first discovered in July 2007 when it stole data from the U.S. Department of Transportation, and gained significant notoriety in March 2009. By that time, around $70 million had been stolen by the virus developers, and it is estimated that one million computers were infected by Zeus.

Conficker was first detected in November 2008, affecting over 9 million computers and causing losses exceeding $9 billion. It exploited vulnerabilities in Windows operating system software. The Bách Khoa Network Center in Vietnam found evidence suggesting that Conficker originated from China, and Vietnam was heavily impacted by this virus. Later, Microsoft released several antivirus tools to ensure protection against the malware.

This virus was developed by the U.S. government and the Israeli defense forces. It was designed as a cyberweapon for warfare purposes. Stuxnet enabled the two governments to detect any nuclear attacks planned by Iran around the world. The virus specifically targeted programmable logic controllers (PLCs), which are used to automate processes like assembly lines or operate centrifuges for nuclear material enrichment.

Mydoom is a computer worm discovered in 2004 that primarily targets Microsoft Windows systems. The identity of its creator remains unknown to this day. It quickly became one of the fastest-spreading email worms, surpassing previous records set by Sobig and ILOVEYOU viruses. The worm would send a message saying, 'Andy, I'm just doing my job, nothing personal, sorry,' causing many to mistakenly think the creator was replying. Mydoom caused an estimated $38.5 million in damages.

As mentioned earlier, Cryptolocker is a ransomware virus targeting Windows operating systems. It primarily spreads through email, often disguised as fake messages or customer complaint letters. Cryptolocker uses encryption algorithms based on Microsoft's CrytoAPI, making it nearly impossible for users to recover their files without paying a ransom. Once infected, the only way to regain access to the encrypted data is to pay the demanded ransom. This virus caused an estimated $20 million in damages.

This virus caused less damage compared to others listed above, and it was first discovered in September 2011. Flashback targeted vulnerabilities in Mac OS X, Apple's exclusive operating system for Macintosh computers. The system would become infected after the user was redirected to a fake website. The malware could switch between different servers, with each switch being based on a unique ID sent to the control server.

This virus is considered one of the most destructive to computers. The ILOVEYOU virus was created in 2000 by two individuals from the Philippines, Reonel Ramones and Onel de Guzman. However, they were fortunate to avoid imprisonment, as Philippine law at the time did not have specific regulations to punish creators of computer viruses. The two exploited people's curiosity by creating files named 'ILOVEYOU.txt.exe,' which took advantage of a flaw in Microsoft Outlook at that time (Outlook being a service that allows users to send and receive emails and access other services like Skype and Facebook). The .exe extension was hidden, and the virus used social engineering to trick users into clicking on a link, claiming it contained all the things they loved. This virus caused over $10 billion in damages.

Code Red is a computer worm that was first discovered on July 15, 2001 by two digital security experts, Marc Maiffret and Ryan Permeh. The virus was named 'Code Red' after the two security experts were drinking a beverage called Code Red when they discovered it. This worm was capable of attacking software developed with IIS (Internet Information Services), which is bundled with certain versions of Windows. IIS is a set of services for servers running Windows, providing and distributing information across the internet, including Web Server and FTP Server functions. The worm spread rapidly by exploiting a buffer overflow vulnerability, using long, repeated strings of the character 'N' to overflow memory, allowing it to run arbitrary code and infect computers. Code Red caused an estimated loss of over $2 billion.

This computer worm is named after a quirky dancer from Florida and was created by David Smith in 1999. The virus caused an estimated $80 million in damages, and Smith was arrested and sentenced to 10 years in prison, in addition to a $5,000 fine. Melissa typically spread through email attachments with subject lines like 'Important message from...' or 'Here is the document you requested...'. The attached files were usually named LIST.DOC. If the recipient opened the file, their computer would become infected with the virus.