If you use Admin Tools, there are reports in the forum that it was vulnerable there are attempts exploit.
the best way to handle it is to update your admin tools to the recent one.
I hope that helps.
I've built many websites but never really got the necessity to use this component! Most says it's awesome but i couldn't understand why I need to make the website more buggy by installing a third party software.
Joomla is secured enough if protected properly.
No software is ever 100% secure, which is why they always need to be updated, patched or bug fixed. Most software developers appreciate exploits reported directly to them so they can patch it and have customers trust they are reliable. as for Joomla, I find it pretty secure, however, there are always potential server and other vulnerabilities coming out everyday in many different ways. Overall, I believe Joomla is safe to use, I have used it.