I once did IT support and I had a client who installed some malware that basically filled up his hard drive with nonsense. That was a lot of data really fast.

I think the point many commenters are making is that yes, lots of data IS necessary to do this scan effectively and quickly, it's not the only heuristic, and it's a bit misleading to compare it to the speed of an MRI given that this does not produce the same data as an MRI.