There are a few things to look for that can indicate a potential malware infection:
Unexpected deny rules on your .htaccess file
Files on your website's root folder that you did not create either manually or via a custom script/cron job
Files such as index.php containing large amounts of unreadable code
Your WordPress admin page does not load the style properly
At Hostinger we have an automatic Malware Scanner on your hPanel that will help identify and remove malicious files on your account, so you will not need to worry about malware infections.
You can find a step-by-step tutorial on how to clean up an infected WordPress site using the WordFence plugin here: WordPress Malware Removal Guide
If your website presents issues after cleanup, you can consider restoring it from a backup. Please note that this would revert any changes you had made after the date of the backup.
To avoid similar issues in the future, we recommend the following:
Use strong passwords: unique, with more than 8 characters using letters, numbers and special characters
Keep WordPress, themes and plugins updated to the latest stable version
Avoid plugins and themes from unknown or third-party providers
Protect your website's contact/registration/login forms with reCAPTCHA