The big issue used to be FTP passwords that were sniffed due to non-encrypted FTP connections, but these days the biggest issue is email. When you configure your mail client (Outlook, MacMail, Thunderbord, Eudora, etc) you need to ensure that you are connecting via SSL or TLS. When you do not connect using SSL or TLS, you send your email address and password across the internet in plain-text for anybody malicious to see.
There are compromised systems out there on the internet that do nothing but sit and watch for email address and password combinations and the result is that the email address is used to send a ton of spam, the hosting account gets disabled/suspended, and the IP ends up blacklisted affecting everybody else on the server. In an event such as this, we very well could charge $75/hour for our time spent cleaning up the black-list and resolving to tickets opened by other customers as a result from such an issue. We really do not want to have to bill anybody for this.
Preventing the issue is so simple, there really is no justification for not updating your mail client to use a secure authentication method. We are looking into the possibility of forcing only secure connection methods, however, we are unsure at this time if the mail software will support such a limitation. In the event that this requirement is put into place, we will email our entire client base a few times over the course of a few weeks advising of the change.
If you have any questions at all, please do let us know. You are welcome to respond to this thread if you have a general question, or to open a support ticket if you have an account-specific question.