Phishing content on my site

Hello,

I started a website a few months ago with wordpress and the theme “Mystique”. It’s a blog with puzzles and I used to post pictures and PDFs on it.

Suddenly my site was suspended and the webhost informed me that I have a phishing content on one of the addresses, which I of course didn’t upload there.

I deleted it but after a few weeks it happened again!

The guys from the webhost told me I might have some “script vulnerabilities”. They also said: “It is possible that the fraudster also installed backdoors which would enable him to regain access to the server at any given time. This usually happens due to outdated software (scripts, applications) installed on the website, which contain security holes fraudsters take advantage of.”

I have no knowledge about webdesign apart from using wordpress and I have no idea what I need to check! I just installed wordpress, chose a theme and started writing a blog…

What do I have to do? I would apreciate any advice… Thanks!!