Top 10 cyberattacks ranked by their estimated nominal dollar cost

The answer depends on what counts as a cost. A global computer worm can generate billions of dollars in estimated cleanup and lost productivity across many organizations. A breach at one company produces a narrower, often better-documented bill. The ranking below uses commonly cited nominal dollar estimates to compare both kinds of attack. It is a guide to their reported economic scale, not an audited league table: estimates for older worms are especially uncertain, and the figures have not been adjusted for inflation.

1. MyDoom: approximately $38 billion

First identified back in 2004, MyDoom propagated via email attachments, infecting systems with extraordinary velocity. Furthermore, it facilitated distributed denial-of-service assaults, wherein numerous compromised devices flood a target with overwhelming traffic.

The frequently cited $38 billion figure reflects an approximation of global damage—incorporating operational disruption and remediation efforts—rather than funds directly stolen by the threat actors. The sheer magnitude of this figure demonstrates how a self-spreading assault can inflict minor financial burdens across vast numbers of victims, even though the exact aggregate remains hard to substantiate.

2. Sobig: approximately $37.1 billion

The Sobig family of email worms circulated in 2003. Its best-known variant, Sobig.F, spread through infected messages and helped turn compromised computers into a distribution network for further malicious activity.

The frequently quoted $37.1 billion estimate combines broad assumptions about infection, lost productivity, and cleanup. As with MyDoom, it should be read as a historical model of global impact, not as a documented bill paid by one organization.

3. Klez: approximately $19.8 billion

Klez started circulating back in 2001 and continued to cause issues throughout 2002. Various strains took advantage of flaws within email applications, capable of masking the true origin of a message, which consequently made compromised correspondence much harder for users to spot.

Its commonly cited cost of about $19.8 billion reflects the cumulative burden of a widespread outbreak: removing infections, restoring systems, and dealing with interrupted work. The estimate is widely repeated but lacks the precision of a modern company’s reported expenses.

4. Sasser: approximately $18 billion

Sasser emerged in 2004 and exploited a vulnerability in Microsoft Windows. Unlike the email worms above, it could spread between vulnerable computers without someone opening an attachment. Its effects included crashes, restarts, and operational disruption at businesses and public services.

An estimated global economic toll of roughly $18 billion is frequently linked to the outbreak. Even in cases where damages defied precise quantification, the takeaway remained unmistakable: unmitigated vulnerabilities could enable malware to spread more rapidly than enterprises were able to react.

5. ILOVEYOU: approximately $15 billion

ILOVEYOU worm emerged in 2000 as an email attachment featuring a seductive message. Upon being opened, the malware propagated across the victim’s address book while corrupting or overwriting specific files. Enterprises globally were forced to take their mail servers offline and sanitize compromised workstations.

Estimates of its damage vary substantially; $15 billion is a commonly cited upper-end figure, not a settled accounting result. The attack remains a defining example of how a simple social-engineering lure can amplify a technical threat.

6. NotPetya: approximately $10 billion

In 2017, NotPetya struck. It initially propagated via tainted updates within popular Ukrainian accounting packages, subsequently sweeping across enterprise networks. Even though it mirrored ransomware, its catastrophic architecture meant numerous targets could not restore their information through extortion payments.

The White House calculated worldwide damages at upwards of $10 billion. Major disruptions hit international enterprises: shipping giant Maersk disclosed that massive segments of its tech framework required rebuilding, whereas various multinational corporations encountered halted manufacturing and logistics. Unlike numerous legacy worm projections, the aggregate impact of NotPetya is backed by considerable publicly disclosed deficits from specific businesses, even though the total worldwide price tag remains an approximation.

7. Conficker: approximately $9 billion

Discovered in 2008, Conficker exploited a Windows vulnerability and built a large network of infected computers. It also used techniques that made removal and containment difficult. Its persistence forced organizations to spend time identifying vulnerable machines, applying updates, and cleaning infections.

A figure near $9 billion is often repeated for its worldwide impact, but the basis for that precise amount is not transparent. Conficker belongs on lists of economically significant attacks; its exact placement in a cost ranking is much less certain.

8. WannaCry: approximately $4 billion

During 2017, the WannaCry ransomware propagated swiftly through the exploitation of a security flaw in Windows. Although it encrypted data and demanded ransoms, the greater financial damage stemmed from halted business operations and subsequent remediation costs.

The United Kingdom’s National Health Service became one of its most visible victims, with disrupted appointments and services. Around $4 billion is a frequently cited estimate of global losses, not a measure of ransom paid. The contrast matters: attackers can collect relatively little while victims bear enormous costs.

9. Change Healthcare: approximately $3.1 billion in reported 2024 impact

A 2024 ransomware assault targeting Change Healthcare paralyzed a significant portion of the medical billing and claims infrastructure across the United States. While medical providers grappled with cash flow problems and billing delays, organizations and patients alike confronted deep anxiety regarding compromised data.

Parent company UnitedHealth Group reported roughly $3.1 billion in 2024 cyberattack-related impacts. That figure is a company-reported financial measure, making it different from the modeled worldwide estimates above. It also does not capture every downstream cost borne by hospitals, medical practices, and patients.

10. Code Red: approximately $2.6 billion

Code Red spread in 2001 by exploiting a vulnerability in Microsoft web server software. It infected vulnerable servers, defaced some websites, and generated traffic intended to overwhelm a target.

Its commonly cited $2.6 billion cost reflects estimates of lost productivity and the work required to protect and repair systems. Like the other early-worm figures, it is best treated as an indication of scale rather than an exact total.

How to read the ranking

These attacks did not all cause loss in the same way. Early worms reached vast numbers of machines, so their headline figures rely heavily on assumptions about time spent cleaning and restoring them. NotPetya combined worldwide spread with severe, documented corporate disruption. Change Healthcare shows how an attack on one critical intermediary can create large costs beyond the company itself.

For that reason, a different method—ranking exclusively audited expenses, adjusting for inflation, or factoring in all indirect costs—would generate a distinct top 10. The underlying theme proves more valuable than the exact sequence: cyber incidents turn out to be costliest whenever they leverage a broadly shared vulnerability or disrupt a service upon which numerous others rely.