Malicious and unused Plugins
Trying new themes as well as plugins is a great way to learn about the new releases first-hand. Once the testing has been done, however, WordPress users can typically uninstall the plugins instead.
Remember that unused or disabled topics and plugins pose a serious threat to the website of WordPress. It is therefore extremely important to immediately uninstall all plugins and themes not used to ensure no information remains in the WordPress server hence why it should be removed. This is a good guide on how to uninstall WordPress plugins correctly.
To ensure that the plugin or theme does not open a new security loophole, always download the latest version of themes and plugins from a trusted partner.