You wouldn't notice ESET's 12% hit unless you were intensively using the processor already. You'd probably notice that full-scan slowdown even if you were just checking email.

But McAfee's full scan hit our test laptop like a ton of bricks, slowing it down by 96%. For example, McAfee Total Protection had a relatively light background impact, slowing down the Lenovo laptop by only 9% after installation. Most other programs were less consistent in their rankings. Kaspersky Security Cloud Free's full-scan system impact was a barely noticeable 6% its quick-scan impact was a barely measurable 1%. It actually sped up the system a bit after installation, indicating that it may be more efficient than the built-in Microsoft Defender Antivirus, which runs by default but deactivates itself if a third-party antivirus program is installed. Kaspersky Security Cloud Free was the undisputed winner in the free categories, beating all rivals in passive, full-scan and quick-scan impacts. Kaspersky did have the second-lightest full-scan impact in the bunch, however. The lightest quick-scan impact among paid programs was held by Kaspersky Total Security at 22%, a percentage that was nearly twice as much as ESET's full-scan impact. That may be because ESET doesn't have a quick-scan option.

Among paid antivirus programs, ESET was not the fastest in all three categories that we measured: passive system impact, full-scan system impact and quick-scan system impact.

Bitdefender 2021 internet security