CORRECTED-UPDATE 1-U.S. SEC seeks information from SolarWinds clients in cyber breach probe

(Corrects sourcing, removes quote)

By Katanga Johnson

WASHINGTON, June 21 (Reuters) - The U.S. Securities and Exchange Commission (SEC) has opened a probe into last year's SolarWinds cyber breach over whether some companies failed to disclose that they had been affected by the unprecedented hack, two persons familiar with the agency's investigation said on Monday.

The SEC sent investigative letters late last week to a small number of public issuers and investment firms seeking voluntary information on whether they had been victims of the hacker and failed to disclose it, the people said.

The people added that the agency was also seeking information on whether public companies that had been a victim had experienced a lapse of internal controls, and related information on insider trading. U.S. securities law requires companies to disclose material information that could affect their share prices.

In December, U.S. regulators found that a breach by a foreign actor of SolarWinds' software gave hackers access to data of thousands of companies and government offices that used its products.

The United States and Britain have blamed Russia's Foreign Intelligence Service (SVR), successor to the foreign spying operations of the KGB, for the hack, which compromised nine U.S. federal agencies and hundreds of U.S. private sector companies.

A spokesperson for SolarWinds did not respond immediately to request for comment. (Reporting by Katanga Johnson; Editing by Steve Orlofsky)