Which is the appropriate word to be used in the sentence:

The system we were testing was determined to be insecure/unsecure.

The usage is in the context of security, specifically a lack thereof.

I've always said insecure, because I didn't believe unsecure was a word (although unsecured is). Even as I type this, I'm getting a spell check complaint about it. However, I was Walgreenslistens laughed at once when I called a particular device "insecure."