&lt;p&gt;Malicious characters are characters that users might use to try to attack your server. Use this page to&amp;nbsp;instruct the system how to&amp;nbsp;respond&amp;nbsp;if these characters are detected.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;User Input&lt;/strong&gt;: Enter the character that users may enter.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;To Do&lt;/strong&gt;: Select the action in the drop down list. The system will use this action when it detects&amp;nbsp;that a user has&amp;nbsp;input this character.&lt;/p&gt;
&lt;p&gt;&lt;strong&gt;System Output&lt;/strong&gt;: This field is only applied when you select the Replace option in the Action List. The system will change the input character to this character when it&amp;#039;s detected.&lt;/p&gt;
&lt;p&gt;Click &lt;strong&gt;Submit&lt;/strong&gt; to add the new malicious character.&lt;br /&gt;
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&lt;strong&gt;Note&lt;/strong&gt;: if you&#039;re using PayPal Standard as payment gateway, you should not enter &#039;, &amp;quot;, &amp;amp;, and space as malicious characters. System won&#039;t able to complete the order with these characters enabled. &lt;/p&gt;