[Jeir]

As others have said, hard cheese, such as cheddar, is fine. The idea that it might 'poison' a hamster is that, like the vast majority of animals, they are lactose intolerant once weaned. Thankfully, aged cheese such as cheddar (especially mature and extra mature) are naturally low in lactose*, so it's safe in reasonable-sized** amounts for hamsters (and other rodents).

*"Enzymes added to milk as part of the cheesemaking process naturally feed on the lactose sugars in the milk developing the flavour of the cheese until the lactose sugar is all naturally used up." - Cathedral City website.
**'Reasonable sized' being about the amount they can hold comfortably between their paws/thumbnail-sized at most for Syrians, maybe half that for dwarfs.