How to prevent .htaccess rewriting?
I am currently managing several of my own sites. Their htaccess files are repeatedly being overwritten to redirect users coming from google searches etc to russian spam sites. I have changed all my passwords, tried every conceivable combination of permissions and contacted my hosting supported and still have no solution. The only way to remove it is to manually rewrite the htaccess to its normal state, which I do, but the malicious conditions are just put in again. 

My questions:

Is there any foolproof way to prevent this? I know that the thumb.php used in wordpress had a bug to allow people to do this, but my install of wordpress has no theme or plugin with thumb.php in any form.

In case there is no solution, is there anyway I could write a small php script to overwrite the htaccess file with the non infected version every 5-6 minutes to minimize the chances of it affecting my users?

Thanks
How to prevent .htaccess rewriting?
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I am currently managing several of my own sites. Their htaccess files are repeatedly being overwritten to redirect users coming from google searches etc to russian spam sites. I have changed all my passwords, tried every conceivable combination of permissions and contacted my hosting supported and still have no solution. The only way to remove it is to manually rewrite the htaccess to its normal state, which I do, but the malicious conditions are just put in again. 

My questions:

Is there any foolproof way to prevent this? I know that the thumb.php used in wordpress had a bug to allow people to do this, but my install of wordpress has no theme or plugin with thumb.php in any form.

In case there is no solution, is there anyway I could write a small php script to overwrite the htaccess file with the non infected version every 5-6 minutes to minimize the chances of it affecting my users?

Thanks