The sheep dip is a computer that is not on the network. It has antivirus and other cyber-security solutions installed on it. Before removable media is allowed back into the company’s networked computer, it is first stuck in the sheep dip computer and scanned for infections much like a real sheep dip removes parasites from a sheep.
Note of caution regarding the sheep dip approach
The sheep dip computer is the first line of defence. So, if it gets infected because the security software doesn’t have the latest definition on it or the operating system does not have the latest updates, then it can become a vector for infection. The sheep dip computer needs to be kept manually updated or placed on a dedicated internet connection.
The protocol may be ignored by staff, who decide not to check the USB flash drive. It is possible to disable the USB ports on their computers. That way they have to go through the sheep dip then a second networked computer to copy the file onto the network.
Computer sheep dips also remove infections.