UK-based telecom giant Colt Technology Services is battling a cyberattack that has disrupted several of its operations for multiple days, including Colt Online, hosting services, porting, and Voice API platforms.
The British telecommunications and network services provider confirmed that the attack began on August 12, with its IT teams working around the clock to contain the impact and restore systems.
Founded in 1992 as City of London Telecommunications (COLT) and acquired by Fidelity Investments in 2015, the company operates in 30 countries across Europe, Asia, and North America. Colt’s network spans 75,000 km of fiber and connects over 900 data centers globally.
Initially, Colt described the disruption as a “technical issue”, but later acknowledged it was caused by a cyber incident. As a precaution, the company took several systems offline, leading to outages in support platforms such as Colt Online and Voice API. Customers are currently unable to use the online portals and have been advised to reach out via email or phone, with delays in response times expected.
Colt emphasized that the affected systems are support services and that its core network infrastructure remains intact. However, the company has not provided an estimated timeline for service restoration. Authorities have been notified, though no details about the attackers or attack method were disclosed.
A hacker under the alias ‘cnkjasdfgd’, allegedly linked to the WarLock ransomware group, claimed responsibility for the breach. The threat actor is reportedly offering to sell one million stolen Colt documents for $200,000. The leaked samples include financial records, employee and customer data, internal emails, executive information, and software development files.
While Colt has not confirmed the breach details, cybersecurity expert Kevin Beaumont suggested that attackers may have exploited a critical Microsoft SharePoint remote code execution vulnerability (CVE-2025-53770). The flaw, patched by Microsoft on July 21, had been actively exploited as a zero-day since July 18.
Beaumont further noted that hackers might have exfiltrated hundreds of gigabytes of sensitive files.
Responding to the claims, a Colt spokesperson told BleepingComputer: "We’re aware of claims regarding the cyber incident. We are currently investigating these claims."
"Our technical team is focused on restoring the internal systems impacted by the cyber incident and is working closely with third-party cyber experts. We are grateful for our customers’ understanding as we work towards a resolution to fix the impacted internal systems."