Just after 'disable_functions = ', write out the functions you want to disable (example: exec,passthru,popen). Here is a list of functions that are commonly disabled as a means to improve security:
7. Click the Save button once you are done.
Important: Some themes, plugins, and features for popular PHP-based website builders (such as WordPress) may rely on one or more of these functions. Disabling these functions may cause certain features to stop working (notably, some WordPress automatic backup plugins).