Well, if it was an effective hack, you wouldn't be able to tell unless the hacker wanted you to know. If he/she wanted you to know, you'd most certainly find out. Sounds simple, but, honestly, the question is still a bit general. If it were posed to you, it was most likely in an effort to generate a dialog between you and the prospective employer, giving you an opportunity to demonstrate your knowledge of hacks without the specific constraints of a "yes" or "no" answer. Employers in such a dynamic field often use these questions without a specifically "correct" answer. Any of the advice already given would probably be along the lines of what would be considered a "good" answer. Good luck in your interview.

Corn