File corruption in all blog sites and MySQL

I have been working against a problem for many weeks now. The files in my wordpress installation are getting a garbled string added to the first line in many of the .php files. This causes errors on all sites similar to this:
Fatal error: Function name must be a string in C:\xampp\htdocs\aureusgroup.blog\blog\wp-includes\option.php on line 1

When opening the files of this installation I see the following on the first line:
[Obfuscated code moderated]

That string is very long and attached to almost every file on our install.

Any ideas? All of the software is running the latest releases (as of July 1st, 2014).

Thanks