Covert channels(c,g,Loki and some distributed denial-of-service tools use the Internet Control message Protocol,or ICMP,as the communication channel between the“bad guy”and a compromicyed system) Hidden text within Web pages Hiding files in“plain sight”(c,g.what better place to“hide”a file than with an important sounding name in the c:\winnt system32 directory) Null ciphers(c,g,using the first letter of each word to form a hidden message in an otherwise innocuous text) steganography today,however,is significantly more(4)than the example about suggest,allowing a user to hide large amounts of information within image and audio.These forms of steganography often are used in conjunction with cryptography so the information is double protected;first it is encrypted and then hidden so that an advertisement first.find the information(an often difficult task in and of itself)and the decrypted it. The simplest approach to hiding data within an image file is called least signature insertion.In this method,we can take the binary representation of the hidden data and the bit of each byte within the covert image.If we are using 24-bit color the amount and will be minimum and indiscriminate to the human eye. A、 B、 C、 D、