The Contact Builder plugin contains one security gap which allows hackers to send spam/phishing emails for account of websites that use it, according to a announcement the company's.
The issue was first reported by some members of the company support forum and soon after by the WordFence team.
According to the company's announcement, immediate measures have been taken to fix all the security gaps and one has been released information.
If you are using Builder Contact in the previous version 1.4.6, you should update immediately to the latest version.
If you have installed the old version of Contact Builder on your server but have not activated it, delete it or replace it with the latest version (do not leave the version containing vulnerabilities on the server, even if you don't have it enabled).
If your subscription has expired and the Builder Contact cannot be updated, contact the company and they will give you the new version for free with a 3 month subscription extension.