The launch of the Galaxy S8 was a key step for the world's largest smartphone maker as it sought to move on from last year's humiliating withdrawal of the fire-prone Galaxy Note 7s, which hammered the firm's once-stellar reputation.
But a video posted by the Chaos Computer Club (CCC), a German hacking group founded in 1981, shows the Galaxy S8 being unlocked using a printed photo of the owner's eye covered with a contact lens to replicate the curvature of a real eyeball.
A Samsung spokeswoman said it was aware of the report and was investigating.
The iris scanning technology was "developed through rigorous testing", the firm said in a statement as it sought to reassure customers.
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Samsung's hopes of competing against archrival Apple's iPhone had been pinned on the Galaxy S8 after last year's Note 7 disaster.
But since it was released in April it has received positive reviews and strong orders.
The CCC previously demonstrated a way to defeat Apple's TouchID fingerprint sensors -- using graphite powder, a laser etching machine and wood glue -- just weeks after the first iPhone 5s hit the shelves.
Traditional PIN protection was "a safer approach than using body features for authentication", Engling said.
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