Boxers are the only type of dog that have ever aggressively attacked my dogs. (two dobermans and a German Shepherd). You have to wonder what they were thinking.
And not just one or two boxers, probably five or six that I have met where we go for grooming and play. This lady is ready to ban boxers completely.
Now, the owners of said boxers are not the brightest light bulbs. They have a tendency to stand there and do nothing about their dogs behavior, so you can see that that is half the problem right there. I would suspect given the natural tendency of the boxer to engage, an owner should be vigilant and not let the dog get the upper hand.
One day these boxers I have met will attack the wrong dog, and something bad will happen. So be sure to keep control !