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ILOVE YOU Love Bug
5. ILOVEYOU (2000)
The ILOVEYOU worm was a devastatingly fast-spreading and effective combo of social engineering and Windows design flaw exploitation. The cost of clean-up and lost work due to the worm, also known as the Love Bug, is thought to total between $5bn and $10bn.
The worm was the work of two Filipino students who were caught, but the case was dropped because there was no applicable law at the time. ILOVEYOU used Microsoft's Visual Basic Scripting (VBS) to forward itself to the contents of the host's Outlook address book. It also overwrote files with copies of itself and tweaked the Windows registry.
It spread around 15 times faster than Melissa, according to the US Army. With at least 50 million computers infected and many large organisations having to shut off internet access, ILOVEYOU highlighted the vulnerabilities within Windows and sparked off large amounts of criticism and me-too infections.
Photo credit: F-Secure