When running in kernel mode rather than user mode, security software has full access to a system's hardware and software, which makes it more powerful and flexible; this also means that a bad update like CrowdStrike's can cause a lot more problems.

Recent versions of macOS have deprecated third-party kernel extensions for exactly this reason, one explanation for why Macs weren't taken down by the CrowdStrike update. But past efforts by Microsoft to lock third-party security companies out of the Windows kernel—most recently in the Windows Vista era—have been met with pushback from European Commission regulators. That level of skepticism is warranted, given Microsoft's past (and continuing) record of using Windows' market position to push its own products and services. Any present-day attempt to restrict third-party vendors' access to the Windows kernel would be likely to draw similar scrutiny. //

For context, analytics company Parametrix Insurance estimated the cost of the outage to Fortune 500 companies somewhere in the realm of $5.4 billion.