The Most Notorious Computer Viruses

Thinking of throwing away your laptop because of a malfunction of some sort? Has a laptop part suddenly stopped functioning properly? Is a program which used to run great suddenly going haywire?

Before you chalk it up to hardware fault like damaged laptop components, you have to first make sure that it isn’t just a virus attack of some sort. While just as harrowing as a laptop part malfunction, viruses can be easily taken care of with a competent antivirus program.

Of course, not all viruses are created equal; and while the viruses depicted below have long since had countermeasures developed for them, at the time of their infestations, they were notorious little buggers.

Here are the five worst of the lot.

1. Melissa

In 1999, a computer virus began spreading like wildfire via email messages. Called “Melissa,” creator David L. Smith said he named it after a Florida exotic dancer. And in the same way that a dancer can allure you with a striptease, the Melissa virus tempted people to open these emails with the message “Here is that document that you asked for, don’t show it to anybody else.” Once opened, the virus then replicates itself by going after the top fifty people in the recipient’s address book.

2. I Love You

A year later, another heavy-hitter emerged, this time from the Philippines. Among other things, it could copy itself several times and hide the replicants in various separate folders; add new files to registry keys; replace several important system files with copies of itself; and download a file called (a password-stealing program) and run it.

3. Klez

In 2001, a year after I Love You hit, a far more sinister one came out of the woodwork. Klez, when activated, multiplied itself through a victim’s email list much like Melissa, and rendered desktop and laptop parts themselves to be inoperable. Before it was totally eradicated, its creators even fine-tuned it so that it would be intelligent enough to copy the email address it was coming from.

4. Code Red and Code Red II

Also in the same year as Klez, the Code Red and Code Red II viruses appeared. These viruses exploited a weakness in the programming of the Windows 2000 and Windows NT operating systems. The weakness in question was the OSes’ buffer overflow problem. This problem occurs when a computer receives more information than the system’s buffers can process and starts to overwrite adjacent memory.

The first Code Red infamously attacked web servers at the White House by implementing a Distributed Denial of Service (DDoS) attack. This attack caused every infected computer to contact the White House’s servers, thereby overloading them.

Meanwhile, Code Red II-infected computers were no longer operable by their owners because the virus created a backdoor program in their computers’ systems, allowing a remote user to gain control of their machines.

5. Nimda

Still in 2001, a virus named Nimda (that’s “admin” spelled backwards) spread throughout the internet. Nimda was notorious for being the fastest-spreading virus then, taking only 22 minutes to get from initial release to the top list of reported attacks.

Despite being able to infect home PCs just as well, its main target was internet servers, with the intention of slowing these down significantly. It travelled through the internet employing various methods, not the least of which was email propagation. This adeptness was what allowed it to multiply itself across thousands of servers in record time.