I know, this might be the wrong project but can't find one for Eclipse IDE Connector.

BTT: It's currently not possible, to add a "private" attachment via Mylin / Atlassian Jira IDE Connector in Eclipse.
As long it is not really necessary for normal attachments, we can upload them via Web-Service and set the permissions ("my staff").

BUT

On issues, customers are involved and we use the quite cool Eclipse integration with the Mylin "Attach context..." feature, there is no way to set the permissions correctly. So any time a developer is updating / attaching these informations, the customer will get an E-Mail and might see this (for him) irrelevant zip file..

I don't know if this is a mylin restriction or if it is possible to you to "fix" this...

With kind regards,
~Marcel