Starbucks Corp (SBUX.O) said on Tuesday that some of its outlets in the United States and Canada suffered payment system outages due to a technology update implemented at store registers.

Multiple users complained on Twitter about the outages and said some stores were giving away free coffee.

"Cash only for today (hopefully)," said a handwritten sign outside a Starbucks at Yonge Street and Erskine Avenue in Toronto.

Starbucks spokeswoman Madeleine Löwenborg-Frick said the company pushed out a software update in line with normal practices and that the outage was unrelated to the "WannaCry" ransomware attack that infected more than 300,000 computers worldwide.

"Our systems have not been compromised by any third party," she said in an email, adding that the company hoped to have all stores back online "shortly."

She did not say how many stores were affected.