Certificate authority (CA) A certificate authority is an entity similar to a notary public. It issues digital certificates, signs certificates to verify their validity and tracks which certificates have been revoked or have expired. Top of Page Digital signature assurances The following terms and definitions show what assurances are provided by digital signatures. Authenticity The signer is ...

Learn how to prevent unauthorised purchases on your Xbox by creating Microsoft accounts for every person who uses that console.

Three ways to add copyright or trademark symbols to your Outlook messages.

瞭解如何在行動裝置、Windows 裝置或 Xbox 主機上兌換 Microsoft/Xbox 禮品卡或其他代碼。

Here are the most likely causes for an unrecognized charge: A Microsoft subscription has recurring billing enabled. Someone you know, such as a family member, bought something with your card. You can now investigate this on the Manage your payments page. A previously declined charge was charged again. A pre-order or split order was shipped. Someone made an in-app purchase from an app, game, or ...

Learn how to use mobile operator billing as a payment option to buy Xbox subscriptions, games, and other content.

針對在 Xbox 主機上購買和使用數位版遊戲的常見問題，尋找相關解答。

Microsoft prioritizes account security and works to prevent people from signing in without your permission. When we notice a sign-in attempt from a new location or device, we help protect the account by sending you an email message and an SMS alert. If your phone number or email changes, it's important to promptly update the security contact info on the Security basics page so we can work with ...

The Microsoft Authenticator app helps you sign into your accounts when you're using two-step verification.

Using Authenticator as a way to sign in If you have turned on passwordless, two-step, or multi-factor authentication for your account, use the following steps to sign-in: Go to the site where you want to sign in. Enter your username at the sign-in prompt and select Next. Select Send notification.