Information leakage prevention method and apparatus and program for the same

An access right to a protected folder (31) is acquired, and when writing designated data contained in the protected folder (31) into a clipboard (22) provided within a main storage device (20), the data is encrypted by using an encryption key associated with the protected folder (31) and the encrypted data is written into the clipboard (22), while when pasting the encrypted data held in the clipboard (22) into a file stored within an auxiliary storage device (30), the encrypted data is decrypted and the decrypted data is pasted into the file. In this way, while retaining the convenience offered by the clipboard, it becomes possible to prevent the protected data from being taken outside the computer system via the clipboard.