The illegal card readers are used to steal the credit and debit card information from customers who use the kiosks to renew their licence plate stickers.
It's still not known how many people may have had their information stolen from the ServiceOntario kiosks.
Government Services Minister Harinder Takhar says the self-serve machines are still being examined to make sure only four were affected.
He says the government is working with the manufacturer of the kiosks to see if they can find a way to prevent the use of skimming devices in the future.
Takhar suggests the province will eventually phase out all of the self-serve kiosks.