[Plugin: WP Super Cache] Web10

Hi,
I have recently found WordPress is saving some of my files into an unknown folder called web10, this has only recently appeared. The folder is not viewable in my ftp program and my webhost does not know what is happening but can see the folder within the cache created by WP Super Cache.

Some of the hits coming back on Google refer to files within the web10 folder and I need to understand what this web10 folder is and is it a problem other than bad permalinks.

Can anyone advise please?
Thanks,
Mickey