Whmcs Code Modification

Question

my company has been using Whmcs for billing what i want to know can i modify the code to my needs (i.e add functionality)i wanted to know that if can do this or not as most part of the code is encrypted. i have just started working on a enterprise level wand wanted to know if i have the full control over whmcs function and can i change,extends or add functionalities

i have been reading forum .and what i get to know that you can't modify the code of whmcs you can just change the looks of whmcs to match your website

so please if any one of you can help me with this to get me started will be great Thanks :)

Answer 1

Well, a few weeks ago a decrypted version of whmcs is exposed, but as you can guess it is illegal to use it. I suggest you to stay with the proper licensed version.

Assuming you will continue with the latest whmcs version, I can say that what you can do is limited. You cannot change the core functionalities but you can easily expand it with hooks and custom modules.

You can change or create you own template.
You can create your own pages(http://docs.whmcs.com/Creating_Pages)
You can use hooks to trigger events within whmcs(http://docs.whmcs.com/Hooks).
You can also create you own modules(http://docs.whmcs.com/Addon_Module_Developer_Docs)

So, if you really need to be independent from the core of WHMCS, I suggest you use your custom software which can communicate WHMCS API only. Use the things you need WHMCS with API only, and if you need something which you cannot do in WHMCS, do that in you custom software. But in this case, you need more time and effort to code your software(probably with your own client interface)

top layer : Your Software(you can code whatever you need) 
middle layer:  WHMCS API
engine layer: WHMCS(you can use the functions of it)

And please be careful, WHMCS is exposed many security problems(sql injection and xss) . So I strongly suggest to use your own software(which you can set your own security), and allow to communicate it with WHMCS API. Don't allow any client's to reach whmcs client area.