Security plugins on your child site can help find security issues and help block specific users, but one thing to be aware of is security plugins which end up causing serious performance issues. One such security plugin is Cerber Security, which has been known to cause performance issues on sites.
Ceber Security plugin will end up making a number of request to plugin files, as well as causing high CPU usage, due to the amount of PHP resources that it ends up using.
When deactivated and uninstalled, the plugin will still leave behind a number of options and database tables. The option values that it will leave behind are as follows;
In phpMyAdmin you can search by option names
ceber% then you can delete all of the created option names.
The database tables to delete (drop) also in phpMyAdmin are as follows;
There are a number of security plugins which can be used in place of Cerber Security, but always be aware that any plugins being used on your child sites can cause knock on issues when it comes to causing performance issues and using CPU resources.