Senator Mark Warner of the Select Committee on Intelligence on Tuesday chaired the panels first hearing on the massive hack of U.

S government agencies and private companies that was discovered in December.

Top executives from Microsoft Crowdstrike Fire I and Solar Winds, whose software was hijacked to breach other companies, said the cyber attack was likely worse than previously thought.

This was an act of recklessness, in my opinion.

Microsoft President Brad Smith said The true scope of the hack is still unknown because most victims are not legally required to disclose information about it and he appealed for government help.

We do need to enhance the sharing of threat intelligence.

But Crowdstrike CEO George Kurtz, whose cybersecurity firm is helping solar winds recover from the breach, turned the blame on Microsoft, calling it's complicated architecture quote antiquated.

Notably the Threat Actor took advantage of systemic weaknesses in the Windows authentication architectures, allowing it to move laterally within the network as well as between the network and the cloud by creating false credentials Impersonating legitimate users and bypassing multi factor authentication.

Amazon Web services was also invited to testify, but the company declined to attend the hearing, irking the senators on the panel, including Florida's Marco Rubio.

Apparently, they were too busy.

The massive breach, which has widely been blamed on Russian hackers, is one of the worst cyber attacks and U.

S intelligence failures on record, affecting at least nine federal agencies and more than 100 U.

S companies, including all four that participated in Tuesday's hearing.