Worst Computer Viruses

Since the dawn of computing for the masses, countless viruses have been released. Today, an estimated one million viruses  are in circulation and thousands are created every month.


Get the inside track on some of the most notable
The Morris Worm(1988)

In 1988, Robert Morris, a university student, released a worm which affected 10 percent of all the computers connected to the internet. The viruses slowed the computers down to a crawl and brought all the machines used by the Massachusetts Institute of Technology to a halt. Within days it became the most widespread virus the world had ever seen, as people shared word documents via email. The concept virus accidentally shipped on a CD-ROM supplied by Microsoft in 1995. It was the first virus to infect Microsoft Word documents. Morris later became an associate professor at MIT.


Melissa was spread via a file to a Usenet group called alt.sex, and the file contained passwords for 80 pornographic websites. The virus was named after a Miami-based stripper. It infected millions of machines. As soon as the email recipient opened the file, the worm attempted to mail itself to the first 50 email addresses it could take from the computer. Its creator, David L. Smith was banned from even going near a computer without consent from a court.

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I Love You(2000)

The “I Love You” virus spread when it was downloaded as an email attachment. It then started copying itself several times and hiding in folders on the hard drive. It did about $10 billion worth of damage, rapidly infecting network’s around the world.

Anna Kournikova(Feb-2001)

Jan de Wit created a virus that tricked the recipient into opening a massage that strongly suggested they would be privy to a glimpse of Russian tennis star Anna Kownikova’s curves. It became so notorious that it featured in an episode of friends.


Nimda is admin spelled backwards. Within 25 minutes of its release it had become the internet’s most widespread worm. It infected email and sent itself out to email contacts, broke into web servers and infected files on websites. It appeared one week after 9/11 leading to speculation that it was created by state actors or even terrorist groups.


It caused about $50 billion worth of damage, rapidly infecting networks around the world. Slammer caused a denial of service on internet hosts and dramatically slowed down internet traffic, infecting most of its 75000 victims within ten minutes. Fifteen minutes after its first attack, the Siammer virus infected nearly half of the servers that hold up the internet.

Mydoom(Jan – 2004)

It was spread through an email attachment which usually had and innocuous title such as ‘Mail Delivery System‘ or ‘Mail Transaction Failed‘. It was the fastest spreading virus of all time. 2.5 million euro reward to find its creator and he was never discovered. It’s aim was to assault google, altavista and lycos and at its peak it managed to shut down google for almost a day. In February 2004 it infected 1 in 12 emails with 1 million interceptions taking place every hour.

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Saseer(Apr – 2004)

It exploited a vulnerability in Local Security Authority Subsystem Services (LSAS). Sasser made it difficult to shut down machines and infected many computers. Its creator Sven Jaschan released Sasser into the wild on his 18th birthday.


It proved that Apple is not so safe after all. After infecting the computer is searched through iChat and sent each person on the iChat list a message which contained a corrupted file that appeared as a JPEG image. Using the iChat instant messaging programme Leap_A spread across vulnerable Mac computers.

Storm Trojan(2007)

Through an email attachment it inundated thousands of computers creating a huge global network of computers enslaved. Each computer would then attempt to infect other computers. It’s peak, up to 10 million CPUs infected. It was eventually contained by antivirus companies.


It caused chaos and panic and Microsoft created a high profile industry group to counter the virus. Appeared in 2008 and infected up to 15 million computers. Its main effected was to prevent people from installing Windows updates and antivirus software. It downloaded additional code that could hijack computers and steal personal information.

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The first virus to specifically target critical national infrastructure. Caused centrifuges at Iran’s Natanz nuclear enrichment facility to spin out of control and effectively self destruct. Widely believed to have been developed by the Israells and Americas to slow down Iran’s nuclear program. Designed to self-destruct in June 2012, it was infiltrated into Natanz via USB stick. A similar attack using Stuxnet was launched at North Korea – it failed.


A particularly nasty piece of malware that made infection personal. Delivered via an email attachment. CryptoLocker would freeze up a user’s personal files including photos and documents and demand a ransom in order to release them. Its encryption method was considered unbreakable causing much alarm and an estimated total ransom of $27 million paid in one three month period. Was eventually halted when it’s database of encryption keys was discovered and posted online. However, it spawned a number of clones that are still active today.


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