Its one of the many threats of a very low hash coin.  Just point 10 Mh/s at some 2 Mh/s coin go drink a few cold ones, come back inject attack, drop your provided net hash to 4...

Its one of the many exploits we will read about in the coming months as some of these coins trickle net hash before dying.

If you have standing 1 satoshi BUYs on weak 30 sat coins you may want to rethink that.