Will it be a bad move for Master's to do summer internship in industry when trying to pursue a PhD program?
A person who has had his finger in both the academic and industrial pie, and then tells me that they want to do a PhD, comes across as more credible. You understand what each has to offer and you are more likely to stick with your choice. As for research ability - it has to be quality, not quantity, at this point. The rest surely will come in the course of a good program. 

If the internship is interesting I would take it. Just make sure you learn something while you are there - do more than "just your job".