ILOVEYOU, sometimes referred to as the Love Bug or Loveletter, was a computer worm that infected over ten million Windows personal computers on and after 5 May 2000. It started spreading as an email message with the subject line "ILOVEYOU" and the attachment "LOVE-LETTER-FOR-YOU.TXT.vbs".[1] At the time, Windows computers often hid the latter file extension ("VBS", a type of interpreted file) by default because it is an extension for a file type that Windows knows, leading unwitting users to think it was a normal text file.
Opening the attachment activates the Visual Basic script. First, the worm inflicts damage on the local machine, overwriting random files (including Office files and image files; however, it hides MP3 files instead of deleting them), then, it copies itself to all addresses in the Windows Address Book used by Microsoft Outlook, allowing it to spread much faster than any other previous email worm.[2][3]