Jetpack email subscription

I would love to know the reason why of my 173 email subscribers only 1 is an identifiable person! Is it some sort of spammers paradise generated by Jetpack?Here is a selection:-

groovyardor670ki38 6 days, 6 hours ago 6 days, 8 hours ago 6 days, 9 hours ago

The last twoe appears on spamlists like here So it looks like it’s best to avoid Jetpac’s Email signup option!

Anyway I’ve deleted it now although there doesn’t seem any way of clearing the existing people.