OPTIONAL>needed of blog commenting enabled
I have cleaned up blogs with hundreds of thousands of comments awaiting approval. So many in fact, that the account ran out of disk space. So it really can clog up your WordPress causing it to stop working making it a real security concern.
In addition to this a percentage of blog spam does contain links to malicious websites.
Assuming you want to continue to enable blog commenting there are many free plugins to help you deal with comment spam. They use different techniques to control spam including captchas. Search these to find one that suits your situation. Make sure the plugin you select is compatible with the latest version of WordPress.
The most common plugin used to counter comment spam is Akismet because it is installed by default with WordPress. In addition to their own identification methods, new spam is identified by the Akismet users as they see and mark comments as spam.
You will need to register for an Akismet.com API key to activate it. This is free for personal blogs but commercial blogs are meant to make a donation. This is not checked so you can use Akismet on your commercial blog without paying.
Do you have an existing problem with a huge number of blog comments awaiting approval?
If you have an existing problem with comment spam there is a plugin to help you clean it up – see the MORE ADVANCED box.
Consider the option of disabling comments altogether.
If you are not sure if you want to have blog commenting enabled then see the MORE INFORMATION box below for a video I made about the value of having blog commenting enabled on most websites today.
Going through and manually deleting them using the standard interface can take many hours, even without attempting to review any, depending on the number of comments you are dealing with.
If you a technically savvy you could go directly to the database and use SQL to purge all comments directly from the database. A method I have used in the past until I found a plugin that did this for me.
This plugin https://wordpress.org/plugins/remove-all-comments/ will remove them but unfortunately it is not tested with the latest version of WordPress. Still if you have this problem I would be inclined to try using it.
A video I made questioning the value of enabling commenting on most blogs today: