Those are Gantry cache files. Using the standard joomla cache mechamisims. These are not hacks. You can turn off Gantry caching in the Gantry admin, but it will slow down your site.
I thought so, however chache files should I expect. Do they not reset (delete themsleves) and create fresh ones? at the moment they just keep adding themselves.
They only get deleteed when the joomla cache is cleared. They get overwritten when the gantry settings are changed and saved. The GantryLess cache files are based on the combination of less/css files needed per page. The less file compilation caches do not get deleted becasuse there is no way to know which combination of less/css files are not needed for a site.