SAN FRANCISCO (CBS SF) — Officials with the San Francisco Municipal Transportation Agency are looking into what caused a malfunction with fare machines at underground stations Friday and Saturday, a Muni spokesman said Sunday.

The malfunction, which began sometime Friday, caused the fare machines at all the underground stations to display the message “you hacked,” according to Muni spokesman Paul Rose.

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The incident resulted in passengers being unable to purchase transit tickets. Despite the malfunction, there was no impact to transit service, Rose said.

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As of Sunday, all fare machines at the stations were back to normal, according to Rose.

The incident remains under investigation, Rose said.

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