WHMCS hasn't been 'cracked' recently. It's been a few years since that whole debacle.
Now, that's not saying WHMCS is (or is not) secure, but it really hasn't been cracked recently. If you're on the latest versions, and keep yourself updated, it's not that hard to keep secure.
Tom Whiting, WHMCS Guru
Linux problems? WHMCS Problems? Give me a shout
Check out my WHMCS Addons
+1 - 866-546-8914 / skype - admin_139201 / twitter/facebook - @whmcsguru