Almost every antivirus scans files on access to ensure malware can't launch, and it also scans the entire system on demand or on a schedule you set. Once cleaning and scheduling are complete, blocking all access to malware-hosting URLs is another effective way to prevent trouble. Many extend that protection to steer users away from phishing sites, which are fraudulent websites that attempt to steal login credentials for financial and other sensitive sites. A few rate links in search results, flagging any dangerous or iffy ones.

Behavior-based detection, a feature of some antiviruses, is a two-edged sword. On the one hand, it can detect viruses that have never been seen before. On the other hand, if it's not done right, it can baffle the user with messages about perfectly legitimate programs.

Any antivirus software should eliminate spyware and other types of malware, but some also include features specifically designed for spyware protection. Features like encryption to protect sensitive data and webcam control to prevent remote spying are available in commercial editions, not free ones. However, some free editions include features like a secure deletion file shredder or a free password manager.

Installing all security updates for Windows, your web browsers, and other popular applications is one easy way to keep your PC protected. Windows 11 makes it easier than ever to stay up to date, but there are still numerous security holes in older Windows versions, popular apps, and add-ons. Scanning for vulnerabilities in the form of missing updates is a feature most often found in commercial antivirus tools, but it can also be found in some free ones. In the list below, you can see which programs include these useful features.

Editors’ Note: Given that the US government has banned new sales of Kaspersky security products, we no longer recommend them.