Any site that runs on a database has the potential to be compromised by this threat.
When a malicious person or script is targeting your website, they try entering certain special characters and strings in any area of the site that accepts user input. These areas are usually Forms for user data such as a login form or comment posts.
When the form is submitted, your site sends the data that is in the text fields to the Database Server in what is called a "Query".
The object of SQL injection attacks is to modify the query so that it runs malicious code. This malicious code varies between attacks, but if successful, it can gain access to all the data in your database, including modifying content.
To secure your site from these attacks, you will have to inspect your coding. Your primary defense is to tell your developer to ensure that your site is safe from SQL Injection Attacks. Most developers will know what this means; any user-inputted data is validated and sanitized to ensure it is not malicious.