Verizon Communications said an attacker had exploited a security vulnerability on its enterprise client portal to steal contact information of a number of customers.
The company said the attacker however did not gain access to Customer Proprietary Network Information (CPNI) or other data.
The vulnerability, which was investigated and fixed, did not leak any data on consumer customers, Verizon said in a statement on Thursday.
CPNI is the information that telephone companies collect including the time, date, duration and destination number of each call and the type of network a consumer subscribes to.
KrebsOnSecurity has learned that a member of a underground cybercrime forum had posted a new thread advertising the sale of a database containing the contact information on some 1.5 million customers of Verizon Enterprise.
The seller priced the entire package at $100,000, but offered to sell it off in parts of 100,000 records for $10,000 apiece, Krebs added.
The irony in this breach is that Verizon Enterprise is typically the one telling the rest of the world how these sorts of breaches take place.