tl;dr: A researcher discovered that the ENUM (e164.arpa) DNS delegations for Saint Helena, Ascension Island, and Diego Garcia pointed to an expired nameserver domain, which he bought for €5, giving him control over phone-call routing lookups for those territories. After initially seeing no traffic and using the domains for personal projects, he later found hundreds of thousands of logged queries—mostly calls to US military bases on Diego Garcia and Ascension—which a malicious actor could have intercepted via MITM. The UK's NCSC eventually took the domain over after he re-reported it, emphasizing military involvement.