ANTS reports the same values here as perfmon would. Unfortunately, Microsoft's implementation of performance counters are glitchy and can produce out of range values like this. Normally it happens if they're read too frequently, but this can also happen at times of high system load.
The same effect will be visible in perfmon, but it's not as noticeable as perfmon overwrites previous data after a minute.
There's not a lot that ANTS can do about this: the most common glitch is to read too low, which can't be distinguished from a valid value. With some counters, like this one, it will 'make up' the 0 values with a large spike - note that the spike is in the middle of a series of values that are 0. The real value was probably constant at 100 over that time, and the performance counter has chosen glitchy values that wind up averaging out to about that over a longer period of time.
Red Gate Software Ltd.