Israeli cyber-security firm, Check Point, warned Sunday that tens of millions of fax machines contain security flaws which enable hackers to connect to private networks.

According to Check Point, hackers send malicious software that a fax machine reads as an image file through the phone line, which is decoded and uploaded in the fax-printer’s memory, enabling hackers to take over the device and enter the network.

Though some modern fax machines have upgrades available to prevent hacks, Check Point reported that Canon and Epson fax machines are still vulnerable, as are older fax machines that do not have updates available.

Fax machines are still widely used in the banking, health-care and law professions, and remain the preferred mode of data transfer in many Israeli government offices.