Timeclock in small office: physical machine vs. software?

The time clock in our office broke. I’m trying to figure out the best solution for replacing it. Software seems like the obvious approach because of it’s flexibility and ease of importing/exporting data, but there may be issues with that solution that I haven’t considered. Are there major disadvantages to using a software time clock vs. a hardware one? Any caveats, disaster stories, etc?

Have any of you had to make the decision between a physical and a software time clock? For those using a software product can you make a positive recommendation for it (or warning to stay away from something you’ve had a bad experience with)? Our office machines are running Windows 7, and I’d prefer to go with a software product that you pay for once instead of a monthly fee to “rent” the software.