Using a standardized open source tool like WordPress gives enormous advantages in stability, development costs etc. But when tools become so widely used, unscrupulous people also start looking at it, trying to find security holes to get access to your server for their own purposes.

The best way to stop that is to use secure passwords and keep WordPress and the used plugins up to date. WordPress has a wonderful built-in feature to take care of updates. Login to administration and go to Dashboard -> Updates and there you have it all within a few clicks.
Some caution though. Make sure you always backup the database and files, since depending on what plugins or adaptations you have, an update may break your site.
Webdesign Costa del Sol offers a service, which includes doing these updates for you. Contact us for more info!