Hepta Contact Pot
This plugin works as a honey pot to catch spam message sent through
Joomla contact forms.
The plugin is installed through Joomla installer as any other Joomla
In the plugin configuration, you may include a list of forbidden words.
Every one of these will be checked in the messages sent through Joomla Contact forms and as soon as one of them is detected, the message will be captured and not sent.
Additional honey pot field
There is an additional antispam measure you can apply, but you need to
override the contact form and add the following field:
<input type="text" name="jform[phone_hepta]" style="display:none
!important" tabindex="-1" autocomplete="off">
This will catch bots trying to send messages to your site, even if they
do not use any of the forbidden words.