A computer worm is defined as a program that has the ability to replicate itself across other machines with or without user intervention. In contrast to a virus, there's no need for a worm to attach itself to a program in order to work. Worms are capable of devastating entire information infrastructures by simply replicating itself and consuming loads and loads of resources or bandwidth. In any event, here's a look at the top ten worst worms in the last twenty years or so.
Released into the wild on November 2, 1988, the Morris Worm was originally made in order to gauge the size of the Internet. However, a coding flaw in the program has inadvertently turned it into an extremely damaging, resource-hogging program capable of bogging down a computer system by infecting it multiple times.
Also known as the Love Bug Worm and the VBS/Loveletter, the extremely harmful ILOVEYOU worm was able to spread like wildfire in 2000 because of its abilities to access the email addresses found in a user's Outlook contact list and send itself infinitely across the worldwide web while overwriting a victim's files.
This Mountain-Dew-named worm exploited a buffer overflow security hole in Microsoft IIS servers and used it to self-replicate into other machines suffering from the same vulnerability. Servers that have been contaminated by this contagion displayed a message alleging that the site was hacked by the Chinese. Within a month, the infected botnets would launch DOS attacks on various online domains, including the one owned by the White House.
A bait-and-switch, faux-porn-list worm that nearly shut down the entire worldwide web when it was released in 1999, Melissa's promise of providing free access to over eighty porno sites enabled it to spread across the mailboxes of affection-starved individuals and mass mail itself into thousands of recipients in a short period of time.
This 2003 malware was able to continue the early 2000's tradition of worm-related chaos by exploiting a vulnerability that Microsoft announced in July of that year. It featured a message addressed to Bill Gates that said, "Stop making money and fix your software," and it was able to infect seven thousand computers within mere hours of its discovery.
This is yet another 2003 worm that was able to propagate itself through millions of computers by posing as a benign email with a rather sinister attachment. The *.pif or *.scr file attachment that contained the malware can insidiously infect any host within its vicinity so long as it's downloaded and run by the user.
This 2007 worm was named after the Kyrill weather storm in Europe. It's a rogue spam that compelled users to open it because it bore a headline alleging that two-hundred and thirty people have died while the Kyrill storm pummeled Europe. Its collection of contaminated machines became part of a large botnet responsible for gathering tons of private data and executing various DDOS attacks.
Even the year 1991 was not spared by the wrath of the computer worm. MS-DOS-based computers were hit by the Michelangelo worm that, as its name suggests, activated on the artist's birthday (March 6). Once it was triggered, this boot sector worm would change the master boot record of infected hosts or overwrite the hard disk.
Jerusalem, which is also known as BlackBox, is believed to be one of the first worms ever detected back in 1987 (it preceded the Morris Internet worm by about a year and is a variant of the Suriv virus). It's a devastating malware that deleted whatever programs or files that are executed every Friday the 13th. It is also capable of increasing the file size of all files running within DOS, which naturally led to slower processing of data and depleted resources.
It is strongly recommended using strong Intrusion Prevention Systems infront of your public servers to the internet.
Always make sure to run up to date Anti Virus on your Windows or Mac OS X.