In simple terms, a virus can aptly be called a virtual disease which affects a computer system and makes it sick, forcing to act in a manner undesired by the user. No good deed goes unpunished, and with the joys and leisure that were brought by the computer, along came the viruses to ruin all the fun. There are billions of viruses out there, big and small. But there were some that stood out and ruined things for us in a spectacular fashion. Below is a list of 10 of the deadliest virus which create havoc in the virtual as well as the real world.

I love you

The three words that can at most motivate you to cross the seven seas - or at least tempt you to open en email. This very temptation was the downfall of many computer users when this multipurpose-multi skilled virus hit the web. It had the ability to replicate itself via IRC chat and email, transfer and hide itself in different files and folders, and infect the registry keys once you opened an email in you inbox declaring “I Love You”. The virus thought to be originated somewhere in the Philippines, caused damage which was estimated to be around $8-10 billion.

Melissa

The creator of this virus received a 20 month jail sentence and a $5000 fine. Generated over a decade ago, this clever piece of virtual disease operated through Microsoft Outlook. This is how it worked: you receive an email titled “Here is the Document you asked for” from an unknown sender, you got infected as soon as you opened the email, and the virus would replicate and delivers itself to the top 50 people on your list without you getting a hint of it. Some major US government departments were hit and the damage is thought to be around $1 billion at least. A 20 month jail sentence well deserved.

MyDoom

 

MyDoom was instigated somewhere in mid 2004 and it actually prompted US senator to propose the creation of a “National Virus Response Centre”. The virus attacked in two phases; the first phase infected different Operating Systems, creating inroads and backdoors and making them vulnerable to external users. Once this problem was sorted out, the MyDoom struck again after few months, this time targeting the Search Engines like Google, slowing them down considerably, and crashing a few.

Nimda

Spell it backwards and you will understand its prime targets: yes, the ‘Admin’ and servers. It was basically a worm and has the record of being the fastest ever virus to spread; it took only 22 minutes to break into the list of top ten most deadly viruses of all times. It basically targeted internet servers and websites, creating a mass crater through which thousands of computers were affected at the same time. Once infected, the systems became exposed to open attacks by the outsiders.

Code Red

Damages of almost $200 million a day, and affecting the computers inside the White House are the degree of achievements of this virus. It subjugated the Windows by acting as a buffer overflow, sending humongous amount of information to the computer so that it spilt over, eventually forcing a shut down by overlapping the memory of the computers. The problem wasn’t solved until Microsoft issued a revival package to cater for this virus.

SQL Slammer/Saphire

Another swiftly spreading virus, it hit 75,000 computers in the first 10 minutes of its inception, taking down and severely damaging numerous American Banks, Security systems and organizations, and Airline networks. And the virus wasn’t just privy to the US; it ruthlessly damaged the internet capacity of South Korea for at least half a day. The damage was estimated around at least a billion dollars.

Storm Worm

One of the latest and most recent viruses to strike the internet, the Storm Worm employed a similar strategy to the one used by the Melissa; the mail’s title mentioned a current natural disaster like an earthquake (but most often a storm). Once the email was opened, the virus spread around like wild fire, affecting registries and documents across the hard disk. It turned out to be a mother-virus, instigating numerous hidden programs in the background which made the PC vulnerable and enticing to hackers.

Klez

With the mix characteristics of a virus, worm and a Trojan horse, Klez gave the antivirus programs a real headache by simply disabling them and making them look like a joke. However this is only the beginning of its trickery; after it was thought it be defeated, it was taken over, decoded and customized by black hat hackers (hackers who specialize in unauthorized penetration). Its ability was enhanced by providing it with the capability to "spoof" from the user's address book and make it look like that an email came from them, increasing the chances of the receiver opening the email and becoming the next casualty.
Sasser
 
Damaging the computer through network ports, Sasser mostly targeted Windows 2000 and XP. It’s main casualties were the news agency Agence France-Presse (AFP) which had all its satellite communications jammed for hours , U.S. Airlines which had to reschedule its flights because of the worm had depleted their computers, a Finnish insurance company which was forced to close down 130 of its offices on emergency basis, Goldman Sachs, and Deutsche Post were all badly affected as well. However its unique feature was that it did not spread through emails, but rather observed computers and kept a look out for their vulnerabilities. On the basis of its knowledge, it would scan random IP addresses from the database and send itself to the next victim.

Autorun

This virus primarily targeted USBs and flash drives and established them as its major source of movement and propagation. It affected networks and all the computers present on them. Once affected, the folder options would be disabled, the task manager too would be unavailable and the virus itself would become the system administrator. The virus would replicate itself in all the folders, therefore eating up useful space on the hard disk and making it eventually extremely slow. The loss was in terms of useful data on millions of computers across the world.