The most destructive computer viruses in history

Posted on Mar 16, 2022      79

In November 1983, American student Fred Cohen created one of the first prototypes of a computer virus.


As conceived by its creators, the Brain virus should become a weapon of retaliation, rather than a cause of chaos around the world

As strange as it may sound, but one of the first viruses, devastating in its consequences, was invented in the name of justice. The Brain virus was created in 1986 by programmer brothers Amjat and Basit Alvi from Pakistan. Their idea was to retaliate against pirates who were stealing their software. But something went wrong, and their program infected tens of thousands of computers around the world.

The virus was written into the boot sectors of 5-inch floppy disks, and when it landed on the computer, it “clogged” the RAM, slowed down the disk, and sometimes prevented data storage.

Most interestingly, the virus contained the information and address of its creators. And when it broke out of Pakistan, the programmers received a barrage of calls asking how to get rid of it. They got so many calls that they finally cut the phone line.


On October 1, 1987, Jerusalem, one of the scary viruses that infected files in MS-DOS, appeared. The trick was that it did not start working immediately, but was activated every Friday, which fell on the 13th of the month, and deleted all the files running on that day.

In that time it infected 6,000 computers worldwide. Estimates put the damage at more than $10 million. It only stopped threatening when the first versions of Windows came out, because it didn’t work on them.

The Morris worm

The Morris worm is one of the first computer worms spread over the Internet, or to be more precise, its prototype: the Arpanet network.

The virus was written in 1988 by Robert Morris, a graduate student at Cornell University. The virus was not supposed to do any harm, only to penetrate all systems and measure the “depth” of the network. But because of a logical error in the code, it endlessly copied itself, filling memory on the computer. Morris tried to fight his brainchild and even sent emails about how to get rid of it, but because of the overload of the whole network, it took 24 hours to get through. The virus was only stopped on the third day.

Although it was extremely difficult to prove that Morris was guilty, his father, an official of the U.S. National Security Agency, insisted that his son confess. The court sentenced Morris to probation, 400 hours of community service and a $10,000 fine. But it had no effect on his career: in nine years he was already a doctoral candidate at Harvard and a professor at MIT.


Once again, this is a case of a well-intentioned virus. It was developed in 1998 by a Taiwanese student, Chen-Ying-Hau, to show the vulnerabilities of his university’s Tatung security system. But again, something went wrong, and his program ended up on the Internet, infecting 60 million computers and causing $1 billion in damages.

The virus was so serious that it even damaged the BIOS chips, so that computers would not start and all information from hard drives would be erased without being restored.


Many U.S. government and military agencies even shut down email to protect computers from ILOVEYOU virus.

One of the biggest epidemics began on May 5, 2000. Filipino students, Reonel Ramones and Onel de Guzman, created the email worm ILOVEYOU. It sent itself to all the e-mail contacts of the infected computer and replaced all the files on the computer with its copies.

In the first 10 days, the number of infected computers exceeded 50 million, and the damage totaled $15 billion! Many U.S. government and military agencies even turned off email to protect themselves against it.

The students were quickly identified but not punished because of the peculiarities of the local penal code, which did not yet have a penalty for computer crimes. As they later said themselves, their goal was simply to test the hypotheses of their thesis.


The MyDoom virus appeared on January 26, 2004 and is considered being one of the most destructive and fastest viruses of all time. It even shut down search engines and reduce all Internet traffic by 10%. Estimates put the total damage at $39 billion.

It was a mail worm that blocked antivirus vendors from accessing sites, changed the registry and made mass mailings.

By the way, be careful! It still exists now because it is autonomous and can live forever as long as email attachments exist.


The epidemic of this virus began on May 12, 2017. It attacked Windows computers, encrypted all files, and demanded a ransom in bitcoins. But even if users paid the ransom, nothing happened.

Within a week, over 300,000 computers in 150 countries were infected. The virus attacked both personal computers at home and corporate ones in hospitals, airports, banks, etc. Some hospitals even had to reschedule their most important operations because of the virus, and many plants and factories deliberately shut down their computers to make sure they were up to date.

The virus was stopped by the blogger Marcus Hutchins, known on the Internet as “MalwareTech”. He analyzed the program code and noticed that the virus was trying to contact a non-existent site And whenever the malware failed to establish with the site, an error would occur and the virus would take effect. The blogger registered the domain of the site with his own money, and immediately after that the spreading of the virus ceased. In addition, Microsoft has released several security updates for various versions of Windows.

According to Cyence, a cybersecurity firm, the economic losses from the virus could be as much as $4 billion.

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