Prevent unwanted software or malware to be installed on your Mac by running as a limited user. Here's how.
Even though malware and unwanted software is less of a concern for Macintosh users, it should still be considered. The growing popularity of OS X gives virus authors more incentive to create malicious software to target Mac users.
A simple way to help prevent unwanted software from being installed on your Mac is to run as a limited user. This may sound complicated but it only requires creating an additional Administrator account to allow your current user account to become a Standard account.
Create a New Administrator Account
The first step to running as a limited user is to create a new account on your Mac to take over the administrator role. To create a new account, open the Accounts preference pane by clicking on the Apple menu, choosing System Preferences, and clicking on Accounts.
Underneath Login Options, click the plus sign. If it is grayed out, you will need to click on the lock symbol and enter your username and password to unlock this option. Once you click the plus sign, a popup will appear asking for the new account information. Be sure to select Administrator in the New Account pull down menu.
Give the new account a username, password, and password hint. Afterwards, click Create Account and your new Administrator account will appear in the list of accounts on your Mac.
More information about creating new accounts is available in this Apple support document.
Switching to Standard User Account
After creating a new Administrator account, you can now switch your current user account from an Administrator account to a Standard account. To switch your account type, reenter the Accounts preference pane and click on your user account. In the Password pane, uncheck the box that says "Allow user to administer this computer". If the option is grayed out, you will need to unlock it by clicking on the lock and entering your username and password.
Once you uncheck this box, a popup will alert you the computer must be restarted before the change takes affect. After saving any open documents and bookmarking all open websites, restart your computer. Once the computer is restarted, your account will be a Standard account.
In creating a new Administrator account and switching your user account to a Standard account, you have become a limited user. What this means is that anytime unwanted software tries to install itself on your system or change one of your system preferences, you will be prompted to enter your username and password. This protects you from unknowingly installing malware or spyware on your Mac or allowing unwanted software to make changes to your system.
There is a downside, however, that comes with running as a limited user. You will always be prompted to enter your username and password when you want to install new software or make a change to your system's configuration. It is up to you whether this inconvenience is worth the protection, but my recommendation is to run as a limited user to prevent your system from being compromised.