I'm getting this patern a lot on Prestashop websites, where thousand, to not say hundreds of thousand, of request are coming from bots not announcing themselves in the User-agent, and coming from different IP's

Very annoying. And you can't filter them because they look like legitimate trafic.

On a page with differents options (such as color, size, etc...) they'll try all the combinaisons, eating all the ressources.