Business Wire, the corporate news release distributor owned by Warren Buffett’s Berkshire Hathaway Inc, on Friday said it had fended off a cyber attack designed to disable it, and that its system was now “stable.”

The “directed and persistent” denial of service attack had begun on Jan. 31, causing Business Wire’s website to slow down, the company said when it disclosed the problem on Tuesday.

In Friday’s statement, Business Wire Chief Operating Officer Richard DeLeo said the company had “successfully mitigated the malicious attempts to render our website unavailable.”

He also said there was no evidence that client information was compromised, and that at no time was Business Wire unable to distribute press releases.

Business Wire is still investigating the cyber attack, and has upgraded its security to avoid similar attacks, DeLeo said.

A majority of Fortune 500 companies use Business Wire, the New York- and San Francisco-based company has said.

Berkshire bought Business Wire in 2006.

A denial of service attack occurs when hackers flood a target with incoming messages, often making it difficult or impossible for legitimate customers to do business.