Settlers knew that the lands that they took or travelled through were already occupied by Aboriginal people. Convicts foraging and exploring from the earliest years had already encountered them; these encounters could be violent, brutal and fatal, or they could be friendly. The Cambridge History of Australia, Volume 1: Indigenous and colonial Australia p 106
Attitudes to Sydney's Aboriginal people hardened in the 1820s and 1830s... they were now considered a blight on Sydney... ibid p 118
On Smallpox:
...The effects on First Peoples, who had no immunity to the virus, were catastrophic. Messengers from First Peoples clans travelled to warn their neighbours of this dreadful disease, unknowingly spreading smallpox themselves... Museums Victoria https://collections.museumsvictoria.com.au/articles/16882