If you're trying out the free Kaspersky antivirus on Windows, & you're using an iPhone & iTunes, you may face a situation whereupon when backing up your phone, there'll be a prompt from iTunes saying the backup couldn't be completed because of insufficient disk space.
I faced that situation a few days ago after installing Kaspersky free, despite having over 300 GB of free disk space. I uninstalled Kaspersky & then reinstalled Avast; the problem disappeared & I was able to backup my phone on iTunes again w/o issues. So if you face the same issue, just uninstall Kaspersky. This is the only antivirus that gave me this issue. None of other antivirus I've used before gave me such a problem.
Other than this problem no other issues but I only tried it for 2 days.