Ever checked that your apache 404 page is displaying porn or cracks?

So folks recently on one of my site when i was updating something,i notices some strange php files with the random numeric names like 32458.php,12135.php and so on.at first i though those were the files related to my sites scripts and i shouldn't be worried about that.but then when i searched in google for my sites suddenly what i have seen was enough to shock me.my site was displaying porn,gambling,cracks, warez.that was a shocking thing my server,my site and they are displaying all such bullshit?
so i decided to look at the files.the link for google land me to some html page in some subdirectory of the site.i immediatly looked in to those diretories and i found no such files.but then the question was how all this porn stuff coming from those sites?another thing i found was that every directory contained .htaccess file which i think i never put and it looked strange to me.so i checked .htaccess file and thats what the root of all the evil.
in tht file all my 404(page not found) pages were getting redirected to the php script which infact was displaying porn and cracks etc.
so lession learned:-
1)Check the permission of your folders.
2)make it a habit of periodically check you site logs and folder for unwanted entities.
3)periodically google for some wared combination like " warez" or " porn" etc.
following is a screenshot for how my site was displaying the pages.(its a google cache)

so wht?its defiantly work of a automated bot,unfortunately i lost the php files otherwise i would have posted them here.
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