Warningwhen click product link

Hi, I am getting this warning when I click on my product links.**

Warning**: Cannot modify header information - headers already sent by (output started at /home/content/b/a/c/backdoor45/html/catalog/includes/languages/english/index.php:1) in /home/content/b/a/c/backdoor45/html/catalog/includes/functions/functions_general.php on line **44

** Does anyone know what this means, and how to fix it?
Thank you, Karole

Check to see if that file starts with <?php or a blank space or blank lines ...

Also check if code has been added to that file ...

If so you want to remove the code added in there before the <?php and check the rest of your site for security issues ...

What version of Zen Cart are you running?

Thank you Ajeh,
the version is 1.3.7

(The <?php had been removed. I know I didn't remove it!
I fixed it, and I will check the security, and be more careful.)

I don't understand what people are trying to gain by hacking into files.
Money? Thrills? Anyway, thanks again, Karole