As a general statement on using custom clients, please note that none of the clients on the forum are endorsed, validated or otherwise checked by Seatribe for defects or malicious code. While we hope that noone would be so dastardly as to post a malicious client here, and while we would, of course, delete the thread on a client found to be malicious, we don't know that in advance.
Be aware, therefore, that a custom client is like any other program you download in that it can steal your passwords, format your hard drive or anything else should its author so wish, and that you should download and run no client that you don't feel that you have strong reason to trust.
It should also be noted that resource files may also contain code that the client will execute, so you should exercise the same caution with third-party resource files as with third-party clients.