Kaspersky wants 10.14 (Mojave), and Avira requires 10.15 (Catalina). Most Mac owners keep the OS up to date, so that shouldn’t be a problem.
To install Avast One you’ll need a Mac running macOS 10.13 (High Sierra). Avast One’s pricing is in line with comparable products. With Norton, which costs $5 more, you also get five full VPN licenses, as well as 50GB of storage for your (Windows) backups. Your subscription gets you a broad range of protection including five no-limits VPN licenses. Note, though, that Clario and Intego charge the same for just three licenses. At first glance, Avast One’s price of $99.99 per year for five licenses might seem expensive. You pay $59.99 for Kaspersky, Sophos, or McAfee, but that price gets you three, 10, and unlimited licenses respectively. Bitdefender Antivirus for Mac, Trend Micro, and Webroot are examples. Quite a few Mac antivirus products, like their Windows cousins, cost just under $40 per year. Do note that once that merger is complete, Norton will own Avast, Avira, AVG, and BullGuard. There’s no visible connection between the release of this new product line and the pending merger of Avast with NortonLifeLock. Best Hosted Endpoint Protection and Security Software.
