I decided to try Defender for the first time today and thought I'd provide some feedback and suggestions.
Installation went smoothly and I like that it guides you through the issues that need attention. I did strike some problems though.
1. As soon as I enabled the blacklist check I got a big red banner saying my site was blacklisted. It's a personal blog with a handful of posts with the last post being from May 2015. I have always run a security plugin on there and it has never been hacked and/or been in any blacklists. I immediately checked it on Google and it was all fine. I then reloaded the defender dashboard and the blacklist status had changed to green and all okay. It's not a good look though - I don't know why it would generate this false positive initially - perhaps it defaults to 'blacklisted' prior to performing the first blacklist check. Either way, if it is happening to others and not just me then it's going to cause a few heart flutters.
2. I tried doing the file scan and after 4% it came up with the 'server resource usage is too close to your limit'. My (CentOS) server is fairly busy and CPU load runs at around 1.5 - 2.5 most of the time. I tried again and it got to 8% before the same error came up. I then went back to the dashboard and it said there were 2 issues in the Wordpress core files. I clicked on the 'Fix' button and was taken back to the scan page which was still showing the 'resource usage' error. I clicked 'Try Again' and then 'Cancel Scan' but each time I clicked the cancel button the page reloaded and the scan restarted. There's no way to stop the scan it seems. I also noticed when I clicked the 'show log' button there was never anything there.
My suggestions for this are:
1. Separate the scan progress log page from the scan page and have it log all activity including the server load at the time the scan is aborted.
2. Provide a setting where I can set the server load threshold that will pause the scan.
3. Separate the scan results page from the main scan page. I have no way of telling which files it thinks are wrong because I keep getting the resource usage error. I really need to be able to see which files have been detected as incorrect and why.