Only the latest version is supported with security updates.
Please contact support with a proof of concept that shows the security vulnerability. Please do not contact us without this proof of concept, as we cannot fix anything without this.
For general opinions on what makes an app more or less secure, please use the forum.
We do not offer a bounty for discovering vulnerabilities, please do not ask. We can however credit you and link to your website/profile in the changelog and release announcement.