Various methods and systems for sharing computer resources and modifying access control rules for computer resources are described. An access control gesture may be defined using a command indicator comprising one or more identifying characters, symbols, or glyphs. For example, an access control gesture may be defined using an @-sign in combination with a modifier that indicates a particular security command to execute and/or a corresponding permission to add/modify/revoke. For example, an input string comprising a plus sign in combination with an @-sign (e.g., “+@”) may indicate a command to add a mentioned user to an access control list. An input string comprising a minus sign, hyphen, or dash in combination with an @-sign (e.g., “−@”) may indicate a command to remove a mentioned user from an access control list. As such, access control gestures can provide a simple and intuitive mechanism to grant temporary access to a designated resource.