In one embodiment, a portable storage device includes a removable device interface and a non-volatile memory having a read-only partition and a regular storage partition. The read-only partition may include a protection program for scanning data in the regular storage partition for viruses. Upon connection of the portable storage device into a computer, the protection program may be read from the read-only partition for loading and running in the main memory of the computer. The protection program may be configured to stop running in the main memory upon removal of the portable storage device from the computer. The device interface may comprise the Universal Serial Bus (USB) interface, for example.