About digital signatures and certificates in Office, and buying a digital certificate from a certificate authority or create your own.

What is Secure Boot? Secure Boot is a security feature in Unified Extensible Firmware Interface (UEFI) based firmware that helps ensure that only trusted software runs during a device's boot (start) sequence. It works by verifying the digital signature of pre-boot software against a set of trusted digital certificates (also known as certificate authority or CA) stored in the device's firmware ...

Get Microsoft billing support. Find help with Microsoft Store purchases, subscriptions, refunds, payment options, and checking your order history.

Learn how to contact Microsoft Store support to get help for your payment and billing issue.

Learn how to find your BitLocker recovery key in Windows.

IMPORTANT You should apply the Windows security update released on July 8, 2025, or a later update as part of your regular monthly update process. This article applies to those organizations who should begin evaluating mitigations for a publicly disclosed Secure Boot bypass leveraged by the BlackLotus UEFI bootkit. Additionally, you might want to take a proactive security stance or to start to ...

Review the warranty terms, check your warranty status, and learn about the protection plans for your Microsoft device or accessory.

Describes how to use the System File Checker tool to troubleshoot missing or corrupted system files in Windows.

在 Outlook 中，有时待发邮件会滞留在发件箱中，无法发送出去。 了解使之发送出去的一些方法。

Microsoft 优先考虑帐户安全性，并且会在未经你许可的情况下阻止用户登录。 当我们发现有从新位置或新设备进行登录的尝试时，我们会向你发送电子邮件和短信通知来帮助保护帐户。 如果你的电话号码或电子邮件发生了更改，请务必及时在 安全性基础知识 页面上更新安全联系人信息，以便我们与 ...