I have noticed that Hashrate has become very irregular, ranging from 1 Mh/s  to an astonishing 4 Mh/s. Why would this happen? I cannot explain that without thinking that some big data center gets in and out the network. Needless to say that when the hashrate is 4 Mh/s is makes no sense for a single average computer to mine since that would not produce a single block in days.