cache/object has gone crazy

We’ve been using w3tc with object cache turned off on a Woocommerce site.

Just recently (about 6 days ago), we got a warning email saying suspected malicious activity. In conjunction with that I was having issues setting folder permissions when doing deployments.

Finally worked out there’s a folder in wp-content/cache/ called object with thousands of folders full of thousands of folders and php files (basically a folder for every hex value, with a folder for every hex value inside each of them, then with a single php file in each folder). I assume this is object caching, but it’s not enabled on our server. Since these folders have been created our server has been running really slowly.

I’ve turned off w3tc, amd have tried to manually delete these folders and files, but there are so many my server crawls to a halt in the effort of it.

Any ideas on

A: What the folder is actually meant for
B: If that’s the correct functionality for the folder
C: If there’s a trick to remove these files and prevent their creation in future.

Thanks