First of all, ChoiceMail itself is virus-free when it is delivered to you. If your anti-virus program is reporting that a virus has been found in ChoiceMail, what has most likely happened is that your anti-virus program found a virus in an email downloaded by ChoiceMail. This is a good thing and not something to be concerned about.

Details
ChoiceMail stores your emails in a folder underneath the one where ChoiceMail is installed. Attachments are extracted and stored in your windows temporary folder.

This actually gives your virus scanner an opportunity to scan those messages for viruses before they get delivered to your mailbox.

This scanning is one if your anti-virus program is configured to check files when they are created. Therefore it happen even if your email scanning feature is disabled.

This is a positive side effect of using ChoiceMail and it actually enhances security on your system.