I believe you're well within your rights to show examples of the work you've completed within your portfolio, with the possible exception of work or information that's protected by Non Disclosure Agreements.
In those instances, it may be best for you to follow up with the company to ensure you have permission to disclose your involvement in performing the work or any other details.
Of course, it may not be likely that you'd be 'caught' presenting such information, but you'll need to cover all of your bases before making a confident decision.
In my personal experience (I am also a software developer), I've kept some project details vague enough that the person I'm speaking with has a general understanding of what the end result was, but not necessarily how it was built or who it was built for.
Ideally, your employers are going to want to know that you have significant experience and are able to perform the duties of the position you're applying for; They will likely understand if you're not able to share the specifics of certain projects you've been a part of.