Horizon Media yesterday confirmed it notified an undisclosed number of people about a January 2026 data breach that compromised their names and Social Security numbers.
Horizon Media calls itself “the largest independent media agency in the world” with $8.7 billion in billings and more than 2,300 employees.
According to Horizon’s notice, an unauthorized actor breached its systems through a “sophisticated social engineering event” on January 9, 2026.
On the same day, a ransomware group called Chaos took credit for the breach. On the group’s data leak website, Chaos threatened to publicly release 3.2 TB of data it claimed to have stolen from Horizon within 48 hours if its demands were not met.
Horizon has not acknowledged Chaos’ claim and Comparitech cannot independently verify it. We do not know if Horizon paid a ransom, how much Chaos demanded, or how many people Horizon notified. Comparitech contacted Horizon Media for comment and will update this article if it replies.
Horizon’s investigation into the January 9 hack concluded on April 6, when it began notifying breach victims.
“On January 9, 2026, Horizon learned that an unauthorized actor gained access to a limited portion of our systems through a sophisticated social engineering event,” says Horizon’s notice to breach victims.
“The investigation determined that an unauthorized actor gained access to a limited portion of our file shares on January 9, 2026, and copied certain files from our system.”
Horizon is offering breach victims 24 months of free credit monitoring through Experian. The deadline to enroll is August 31, 2026.
Chaos is a ransomware group that first surfaced in 2021 but didn’t start claiming victims on its data leak site until March 2025. The group attacks both individuals and organizations through drive-by-downloads and phishing. It employs a double-extortion scheme in which victims are extorted both for stolen data and to restore infected systems.
In total, Chaos has claimed responsibility for 51 ransomware attacks. Of those, 13 have been confirmed by the organizations it targeted.
Service-based businesses like Horizon Media are frequent targets for Chaos. Some of the group’s other attack claims include:
In 2026 to date, Chaos has claimed another 17 attacks, two of which have been confirmed so far.
Comparitech researchers have confirmed three ransomware attacks on service-based businesses like Horizon Media in 2026 to date. In addition to Horizon and NELSON, Blanchard Training & Development notified 310 people of a March 2026 data breach claimed by the Payouts King ransomware group.
Ransomware attacks on businesses can both steal data and lock down computer systems. Infected businesses must then either pay a ransom or face extended downtime, permanent data loss, and putting customers and/or employees at increased risk of fraud.
Other recently confirmed ransomware attacks in the US include:
In 2026 to date, we’ve logged 85 more confirmed ransomware attacks on US businesses.
Founded in 1989, Horizon Media is headquartered in New York and has offices in Los Angeles and Toronto. According to its website and LinkedIn profile, it generated $8.7 billion in billings and has more than 2,300 employees. Horizon says it is “the biggest independent media agency in the world” and “the third-largest U.S. media agency, according to COMvergence data.”
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