All Mac antivirus software packages find viruses using both on-demand- and always-on protection. The former examines individual files either during scheduled scans or when you decide to run one. This can take a long time, especially if you have a lot of files, and some antivirus products will hog your Mac's processor power to prioritize the scan, so it's worth selecting a convenient time. (See how to scan a Mac for malware).

Always-on malware protection protects you when a scan is not currently active. If malware arrives - perhaps via an email or a downloaded file - your antivirus software should detect and quarantine it. Quarantining a file involves moving it to a safe folder, allowing you to decide what to do with it. You'll typically receive a notification of the discovered malware, but some Mac antivirus products can be more informative than others in these notifications (something we keep in mind in our testing).

The effectiveness of this on-demand and always-on virus protection is absolutely the most important thing when it comes to choosing Mac antivirus, but additional features may also affect your choice.

Many Mac security suites now include ransomware protection. Ransomware is a type of malware that encrypts your files and demands a fee to decrypt them. An anti-ransomware feature will typically block any app from writing to a user's home folders, such as Documents or Photos, unless that app has been whitelisted. Some apps, such as Microsoft Word, are pre-approved, and you can whitelist any that you trust.

Web protection via browser plugins or extensions is also a common component and aims to stop you (or your children) from visiting infected websites or handing over personal information when you shouldn't.

Plenty of Mac users will tell you that Apple computers are inherently secure and don't require protection beyond the software already provided by Apple. We'd argue that they are wrong, or at very least overconfident.

Macs are generally more secure than their Windows brethren because macOS is a Unix-based operating system, which means it is sandboxed. This is like having a series of fire doors: even if malware gains access to your Mac, it is unable to spread to other areas of the machine. But while they are more difficult to exploit than Windows PCs, it is not impossible.

You can read more about this topic in our article do Macs need antivirus? More general advice can be found in our Mac security tips; and those who have been hit by a malware attack should see how to remove a virus from a Mac.

Using a Mac antivirus product, especially one that includes tools to improve your online privacy, may lull you into believing you’re completely safe from personal and private information leaking out and that you no longer need to keep your wits about you. That’s not quite the case. While there’s no reason to panic, you should still practice caution - and there are a few more issues you should consider when using Mac antivirus, too.

First, an antivirus for Mac product may upload the complete text of files flagged to the cloud, where it can be analyzed by separate tools hosted there. This practice is normal and sensible: some malware can detect when a running process may examine it, and will then engage in subterfuge. Antivirus software makers also can access their massive databases to examine files with characteristics that trigger their algorithms - certain elements that match known malware. As a result, security researchers discover new viruses, worms, Trojans horses, and the like. However, helping the greater good means you’ll have to be comfortable with trusting a third-party with your file contents. Where appropriate, we noted privacy policy issues in individual reviews.

Second, this software may also rely partly or entirely on cloud-based checks of URLs, malware, and the like. Accordingly, an antivirus package might upload every URL you visit, metadata about files, signatures of files, information about your computer’s hardware, a list of running or installed applications, and more. Companies vary on their disclosure of such policies, and may not let you opt out of this kind of sharing. We note issues in each review as appropriate.

Third, antivirus software makers also get a sense of what behavior is happening on your computer that’s being monitored or blocked, and may use that information for their own purposes. In some cases, you can opt out of this information gathering.