There are four major independent institutes that conduct antivirus testing and report test results: AV-Comparatives, AV-Test Institute, SE Labs, and MRG-Effitas. These labs have the resources to test thousands of real, active malware samples of all kinds (viruses, worms, ransomware, zero-day exploits, Trojans, botnets, backdoors, and more) and to perform the same tests on different antivirus software simultaneously to guarantee accurate comparisons.
These labs are certified by independent auditors, and many work with universities to ensure state-of-the-art testing methodology. Independent test labs charge the antivirus companies to participate in these tests. Major AV brands consider this a necessary expense in order to verify the efficacy of their products. So when a company has no recent test results to show, it should arouse suspicion.
Well-known reviewers, such as Neil J. Rubenking of PCMag, use a combination of independent test results, their own hands-on testing, and personal experience with a product’s usability and bonus features to judge the best antivirus software.