As I indicate when I create an HTML mailmerge to an email the file created has appended to the bottom of the all records of the database.
I will leave this up to your determination as to whether or not this is a security issue.
"the file created has appended to the bottom of the all records of the database."
I don't understand the problem, can you re-phrase this with all the steps you used to arrive at a situation where you think there "is a security issue."
Tools -> MailMerge -> Use the current document -> Next
E-mail message -> Next
Select Address List (Select the Address database and table that you want
Filter if you want to by click on filter) -> Next
(Create a salutation if you want to) -> Next
(Preview and edit the document if you want to) -> Next
(Personalize the mail merge) -> Edit individual document -> Scroll down the
document and records in the database are in the document in table form ready to
be sent along with the document (Note: this could be a result of filtering
since before I make myself look silly I need to check if things look OK so I'm
sending a mailmerge email to myself). -> Next
POTENTIAL SECURITY ISSUE
If the personalized data of other people are accidentally sent via email that data could potentially be sensitive or confidential. In such a case, it could disastrous if that data got out don't you think.
Getting the entire contents of the database dumped at the end of the file sent out to everyone included in the mail merge would definitely be a bug, but this doesn't happen for me though when I try it from scratch
Try filtering out 1 email address from the list.