Computer viruses are the malicious software or code written by programmer with ulterior motives to harm the computer or its software program. A computer infected with virus cannot function properly like a normal computer and it has problem during execution. Though computer viruses are around from the time computer was invented but with each passing year, the intensity of the attack has increased considerably. Now it is estimated that computer viruses cause loss of billions of dollars every year.
Below are top 5 viruses that really made people sit down and take notice of them seriously. These viruses almost crippled the entire computer network system, have a look at them.
1. Trojan Horse or Remote Administration Tool or RAT (2002)
What is Trojan Horse?
Trojan horse is fiercely deadly malicious software which infects your PC once you execute the virus. Once you have executed it start making copy of itself in multiple directories which makes difficult to be removed from the system. It had the ability to steal your confidential data through keystroke logging or damage your computer completely. Written in Delphi programming language it is still considered one of the mostly deadly viruses ever built for computer.
It used to inject viruses into specific process like “explorer.exe” (Windows Explorer), “iexplore.exe” (Internet Explorer), or “msnmsgr.exe” (MSN Messenger).
What it could do?
a. Access file manager
b. Get screenshots of your PC
c. steal password
d. shut down, reboot, logoff or crash your PC
2. SQL Slammer or Worm.SQL.Helkern (2003)
What is SQL Slammer?
SQL Slammer is another dangerous virus which spread like a wildfire and caused much damaged. As per some humble estimates the virus spread over 90% of the host within 10 minutes and infected around 359000 PCs and caused economical damage around $1.2 Billion. This virus slowed down Internet traffic and denied services on some internet host.
3. MyDoom or W32.MyDoom@mm (2004)
What it MyDoom?
MyDoom affected mainly Microsoft Windows and spread everywhere through mail attachments. Users got an email with the subject as Error or mail delivery, test, or mail transaction failed in languages like English or French. If a person went ahead clicked the file then the virus used to resend the mail to all the address which were there in users contact details. This virus is speculated to come from Russia and caused damaged worth $38 Billion.
4. Bandook Rat or Backdoor.Win32.Bandok.bd (2002)
What is Bandook Rat?
This is another virus similar to Trojan horse but with added destructive features. This virus infected Windows NT, 2000, XP, 2003, Vista, Windows 7 based computer system.
What it could do?
a. Create the server component
b. Firewall bypass
c. Reverse connection
d. Different installation path
e. Capture of screen shots
5. BlackWorm or I-Worm.Nyxem (2006)
BlackWorm computer virus spread in mails using an external SMTP engine. It had the ability to send itself by different subjects, body text and attachment names. Once installed the virus copies itself multiple times to infect hard disk, and is hidden in disguise. The virus was meticulously designed to infect and corrupt the data on 3rd of each month. It is estimated that 300,000 unique IPs were affected.
