1. Elk Cloner (1982)A first of its kind, the Elk Cloner didn’t harm a lot of computers, but it did set an unsettling precedent as the first wild virus, one that can freely spread on its own. Created by Richard Skrenta, a computer savvy high school prankster, it merely infected boot sectors, featuring a threatening message that read “It will get on all your disks. It will infiltrate your chips. Yes it’s Cloner!” Fittingly, Skrenta is now a computer programmer and Silicon Valley entrepreneur with extensive experience in the industry.

2. Brain (1986)Viruses were made more complicated and resilient with the formation of Brain, the first full-stealth virus capable of evading early disk utility programs. Infecting floppy disks, it caused only minor problems, as it slowed the disks and sometimes made them unusable. Brain originated in Lahore, Pakistan and its effects surfaced in 1987 and 1988, when infections were discovered at the University of Delaware and the Providence Journal-Bulletin, the latter of which experienced the deletion of work as a result. Today’s viruses that refuse to die are all grandchildren of Brain, which is why it will forever be considered among the most disruptive - it bred them.

3. Morris Worm (1988)The sanctity of the Internet was breached with the proliferation of the Morris Worm, which garnered mainstream attention because it resulted in the first US conviction under the 1986 Computer Fraud and Abuse Act. By attacking vulnerabilities in Unix sendmail, finger and rhs/rexec multiple times, it could cause programs to become unusable. Approximately 6,000 UNIX systems were infected by it, a disruption that couldn’t be ignored. Creator Robert Tappan Morris, a student at Cornell University, was convicted and sentenced to three years probation, 400 hours of community service, and given a $10,000 fine. Currently, the former outlaw is a tenured professor at MIT.

4. CIH Virus (1998)As the internet was rapidly expanding in the late ’90s, the first truly feared viruses emerged. The CIH virus did the most damage, as it overwrote critical information in system drives and corrupted system BIOS. Present in several thousand IBM Aptivas, it first surfaced on a large scale in Asia - it was created in Taiwan by Chen Ing-Hau - destroying numerous PCs. Measures of protection were implemented, but the virus returned in varying forms in the early 2000s.