Pal Pay PHP Error

Site in question: http://mapletonvetplex.com/

I hope I'm posting this to the correct section. I've inherited the maintenance of a Zen Cart site. It's been up for a few years with no real issue. The owner of the site then got reports that Pay Pal (the only payment option the company offers) wasn't working. When I click on the "Pay Pay IPN" option I get the following error:

Warning: require(/home/content/j/b/r/jbryk/html/includes/modules/payment/paypal.php) [function.require]: failed to open stream: No such file or directory in /home/content/j/b/r/jbryk/html/admin/paypal.php on line 55

Fatal error: require() [function.require]: Failed opening required '/home/content/j/b/r/jbryk/html/includes/modules/payment/paypal.php' (include_path='.:/usr/local/php5/lib/php') in /home/content/j/b/r/jbryk/html/admin/paypal.php on line 55

The other odd part is that "Visa" and "MasterCard" were now selected as payment options. The company has never offered this option.

I don't want to sound paranoid, but could this be a sign of being hacked? Can anyone suggest a solution for my PayPal error?

Thanks
Jarrod

My guess is that your 1.3.8 version has been hacked. I would shut the site down until you determine whether that's true.

http://www.zen-cart.com/wiki/index.php/Recovering_From_Hacks

You also haven't changed your admin folder name, which may be the way they got in.