Most websites require their images and temporary directories to have full write access to store files generated by the site. However, vulnerabilities in the website's code can allow hackers to upload malicious PHP or Perl scripts into these directories, potentially leading to issues such as email spamming campaigns.
To avoid this:
Create an .htaccess file with the following content and save it in each directory you wish to secure:
<Files "*.php">
Deny from all
</Files>
<Files "*.pl">
Deny from all
</Files>
Allow from all