2000 · Security

The ILOVEYOU virus: the love letter that infected the world

Last reviewed 16 October 2026

In May 2000 an email titled “ILOVEYOU” spread from the Philippines to tens of millions of computers in days, overwriting files and flooding mail servers.

What happened

On 4 May 2000, people began receiving emails with the subject line “ILOVEYOU” and a short message asking them to read the attached love letter from the sender. The attachment was named LOVE-LETTER-FOR-YOU.TXT.vbs. It came from someone the recipient knew, because the worm sent itself to every contact in the victim’s Microsoft Outlook address book.

The outbreak started in Asia and followed the working day west. Within hours it reached offices across Europe and then North America as people arrived at work and opened their mail. Organisations including the UK Parliament, the Pentagon and large companies shut down their email systems to stop it spreading.

How it worked

The attachment was a Visual Basic Script, not a text file. Windows hid known file extensions by default, so many people saw only LOVE-LETTER-FOR-YOU.TXT and assumed it was harmless. Double-clicking it ran the script with the user’s full permissions.

Once running, the worm copied itself into Windows system folders, added itself to the registry so it started with the computer, and mailed itself onwards through Outlook. It also overwrote many files on local and network drives with copies of itself, including JPEG images and scripts, and hid MP3 files. For many victims the lost photos and documents were the real damage.

An earlier version also tried to download a password-stealing program, which pointed investigators towards the motive: collecting dial-up internet passwords.

The scale

Estimates at the time put the number of infected machines in the tens of millions, often quoted as around 10% of computers connected to the internet. Estimates of the cost of lost work and clean-up ran into billions of dollars. Dozens of copycat variants with different subject lines followed within days.

Who wrote it, and why no one was convicted

Investigators in the Philippines traced the worm to Manila. Suspicion fell on Onel de Guzman, a computer-college student whose rejected thesis proposal had described a program to steal internet passwords. Charges against him were dropped because the Philippines had no law against writing or spreading malware at the time.

The case pushed the country to pass its Electronic Commerce Act weeks later, in June 2000, which made hacking and virus spreading crimes. Decades later de Guzman told a journalist he had written the program to steal dial-up passwords because he could not afford internet access, and that it spread much further than he intended.

What it changed

ILOVEYOU made social engineering the centre of email security advice. It did not exploit a software bug; it exploited curiosity and trust. Mail gateways began blocking script attachments such as .vbs, Microsoft tightened Outlook’s handling of attachments in later updates, and “do not open unexpected attachments, even from people you know” became standard advice.