Hackers penetrated the computer network of a Verizon Communications subsidiary, but the company says it plugged the hole before much data was compromised.

Verizon Enterprise Solutions in Basking Ridge, N.J., confirmed the breach, and said it recently fixed a security vulnerability on its enterprise client portal. The attackers were able to access corporate customers' contact information before Verizon fixed the problem. The breach was reported earlier by Krebs on Security.

"Our investigation to date found an attacker obtained basic contact information on a number of our enterprise customers," Verizon said in an emailed statement. "No customer proprietary network information or other data was accessed or accessible. The impacted customers are currently being notified."

Verizon Enterprise Solutions provides services to Fortune 500 companies, including financial institutions. One of its services is advice on how to defend against data breaches.

Data from consumers was not involved in the breach, Verizon said.

The hackers posted an advertisement this week on an online forum for cybercrime, in which they said contact information on about 1.5 million customers was for sale, Krebs on Security reported. The hackers said the entire data stash was available for $100,000; or, the data could be divided into sections of 100,000 customers, with each selling for $10,000.