There are a few basic indicators that might help you determine if your WordPress site has been hacked or infected.

1. A Sudden Decline in Web Traffic

If you see a dramatic decline in traffic in your analytics statistics, it's possible that your WordPress site has been hacked.

2. You're unable to access WordPress

If you are unable to enter into your WordPress site, it is possible that hackers have erased your WordPress admin account.

3. Bad Links Have Been Added to Your Site

Hackers may install a backdoor on your WordPress site that allows them to change the files and database.

4. Your homepage has been tampered with

Some hackers might usually alter your homepage with a message of their own. Some may even attempt to extort money from webmasters.

5. Your Server Has Unknown Files and Scripts

Using a site scanner plugin like Sucuri, detects an unfamiliar file or script on your server, it will notify you.

6. Your website is frequently slow

Hackers may send an excessive number of requests to your server. Such behaviour will cause your website to become slow, unresponsive, and inaccessible.

7. WordPress Emails Aren't Being Sent or Received

If you can't send or receive WordPress emails, it's possible that your mail server has been hacked to transmit spam.

8. Hijacked Search Results

If your website's search results show false titles or meta descriptions, it's a clue that your WordPress site has been hacked.

9. Popups or Pop Under Adverts on Your Website

These types of hacks try to gain money by diverting traffic to their own junk ads.