CrowdStrike is blaming a bug in an update that allowed its cybersecurity systems to push bad data out to millions of customer computers, setting off last week’s global tech outage that grounded flights, took TV broadcasts off air and disrupted banks, hospitals and retailers.

CrowdStrike also outlined measures it will take to prevent the problem from recurring, including staggering the rollout of updates, giving customers more control over when and where they occur, and providing more details about the updates that it plans.

The company on Wednesday posted details online from its “preliminary post incident review ” of the outage, which caused chaos for the many businesses that pay for the cybersecurity firm’s software services.

The problem involved an “undetected error” in the content-configuration update for its Falcon platform affecting Windows machines, the Texas-based company said.

A bug in the content-validation system allowed “problematic content data” to be deployed to CrowdStrike’s customers. That triggered an “unexpected exception” that caused a Windows operating system crash, the company said.

As part of the new prevention measures, CrowdStrike said it’s also beefing up internal testing as well as putting in place “a new check” to stop “this type of problematic content” from being deployed again.

CrowdStrike has said a “significant number” of the approximately 8.5 million computers that crashed on Friday are back in operation as customers and regulators await a more detailed explanation of what went wrong.

Once its investigation is complete, CrowdStrike said it will publicly release its full analysis of the meltdown.