I have noticed a plugin on my website that I did not install myself. It is under 'drop-in' plugins, not in the normal 'active' plugin list. 

It is called 'object-cache.php
Memcached Redux'. This is its website  https://wordpress.org/plugins/memcached/

My host told me it was last modified on 10th July when I first installed soledad theme. Is this plugin part of the theme?

I am worried because I have not installed it myself, and I do not know how it has got there.

Any help would be greatly appreciated.

Regards

Joe