More than 3500 McDonald's customers in Perth were ripped off for millions of dollars by criminals who switched Eftpos card readers and replaced them with lookalike skimming devices.

Revealing the gang's methods, Western Australia Major Fraud Squad officer, Det Sr Sgt Don Heise, said it was likely that McDonald's staff in a number of restaurants were distracted somehow while the switches were made.

The bogus devices could be plugged in and transmitting customer card details to the gang in less than half a minute.

It is understood that customers were taken for more than $4 million.

McDonald's has been urgently reviewing its Eftpos security measures across Australia and will soon be upgrading its systems.

Meanwhile, WA police have set up a task force investigate the scam.

Source: WA Police