Top 5 Most Dangerous Computer Viruses of the Decade

1. Sadmind worm (2001)
ALIAS: Sadmind/IIS, Unix/Sadmind, Solaris/Sadmind.worm
The Sadmind worm was a self-propagating piece of malware, It was first discovered on May 8, 2001 in china. Sadmind is designed to provide remote system administration operations and is installed by default with many versions of the Sun Microsystems operating system. It affected some big operating systems like Sun Microsystems Solaris(OS) and Microsoft's Internet Information Services (IIS) which is the world's second most popular web server in terms of overall websites behind the industry leader Apache HTTP Server.

2. Beast Trojan (2002)
Beast is a Windows-based backdoor trojan horse more commonly known in the underground cracker community as a RAT (Remote Administration Tool). It was created in Delphi and released first by its author Tataye in 2002. Beast was one of the first trojans to feature a 'reverse connection' to its victims and once established, it gave the attacker complete control over the infected computer.
Once connected to the victim computer, via Beast hacker can access victim's all computer file and directories along with the power to upload, download, delete or execute any file or folder.

3. SQL Slammer (2003)
ALIAS: Sapphire, Worm.SQL.Helkern, SQLSlammer
Appeared first in 27th January 2003 and soon got a high rank in the list of most dangerous worms of the year because it is the first fileless worm. Slammer was able to spread by taking advantage of the vulnerability found in the SQL Server.

Slammer spread to over 90 percent of all vulnerable hosts in 10 minutes and infected around 359,000 computers total and according to London-based market intelligence the worm caused between $950 million and $1.2 billion in lost productivity in its first five days worldwide.

4. Sasser (2004)
Sasser is an Internet worm that probably caused around $18.1 billions of dollars of damage in 2004. It was created by a Computer science student, Sven Jaschan in Germany first seen on last day of april. While there was no intentionally destructive payload, Sasser did cause many computers to slow down or crash, causing some high profile damage.
And was destructive enough to shut down the satellite communications for some French news agencies. It also resulted in the cancellation of several Delta airline flights and the shutdown of numerous companies’ systems worldwide.

5. Bandook (2005)
ALIAS: Bandook Rat
Bandook Rat is a backdoor trojan horse that infects Windows NT family systems (Windows 2000, XP, 2003, Vista). It uses a server creator, a client and a server to take control over the remote computer. It uses process hijacking / Kernel Patching to bypass the firewall, and allow the server component to hijack processes and gain rights for accessing the internet. It is somehow very similar to Beast Trojan (2002)