As the fall semester comes to a close, I have begun to update my resume, and start to submit it to companies for summer internships. I worked for a large company last summer as an Engineering intern, but I'm having trouble explaining my duties.

Basically, the interns were there to fix bugs that the regular programmers were too busy to work with. Much of these were trivial, but some of them were very complex, and I learned a lot from them. However, without talking about source code and system design, it's hard for me to explain my job in terms other than "I fixed stuff that I was told to." This is pretty standard for interns I would imagine, but it's hard to make look good on a resume. While the interns were rarely tasked with writing system components from scratch (I don't have access to any of my code anyway), I also collaborated with the other interns and we solved many problems, including the hellish task of combining the alarm systems from multiple systems.

How can I show this on a resume without having proof? This might be a fundamental trouble for all programmer resumes, but any advice would be welcome.