The short answer is yes! If you run a temp or permanent staff Agency and have personal data of any type entered or available by or through that site, you should be very worried.
This is why.
WordPress is open source. To most people that means nothing but maybe it sounds good? Even better there are lots of free WordPress plug-ins - What could possibly go wrong? Well for “even better” read “even worse!”
Open source means that all the code (stuff that makes it work) that goes into any WordPress is available to anyone who wants to look: not many. You could look, any five year old kid could look. Probably they may be able to understand is going on better than you or I. Let’s face it: if you got even a popular novel in a language you couldn’t read, you wouldn’t continue, you’re not a masochist and there are other web sites for that!
It gets worse, even though you might read it, and understand it, so you can also change it! For open source there is no guarantee that anyone other than the (last) author has read (and understood) it. No guarantee that what is there is goof for you and your site. Open source is considered good because its assumed someone with good intentions has read the code and held up a hand to say if it’s bad. Usually this does just not happen!
A few years ago a person who we probably should assume had malevolent intent did this for an open source security system and left it riddled with flaws. This went undiscovered for years. Only now is that security system being carefully controlled by a multi-million pound group funded by a group of large concerned software companies who use it. Only now is it considered reliable.
It is certain that similarly some WordPress add-ins or plug-ins have been written specifically to appear attractive and open up the end user to all manner people hacking their sites. Many users see “free WordPress plugin” and think what could possibly go wrong? I’ll install that! So they add at least one bad hack to their site and probably the world’s supply.
Hackers 1 Security 0
This actually happens on a major scale every few years.