[pricemm]

I found iThemes security on a simple search and it has really good reviews

https://wordpress.org/plugins/better-wp-security/

Does anyone know of a better free plugin to recommend?

[TKmeridian]

I'm currently using Wordfence Security and they provide very good protection and feedback as to who is attacking our site. It is very highly recommended by many WP users and it was recommended by a digital marketing friend of mine who maintain website for a living. So I guess it is worth looking into :)

[binil]

Wordfence is a pretty comprehensive plugin and it will need more resources.

Another plugin that I suggest is https://wordpress.org/plugins/block-bad-queries/
Its pretty light.