Một ngày đẹp trời tôi đọc được một email với nội dung khó hiểu:

“Dear Friend , Especially for you - this red-hot intelligence
. If you no longer wish to receive our publications
simply reply with a Subject: of “REMOVE” and you will
immediately be removed from our mailing list . This
mail is being sent in compliance with Senate bill 1623
, Title 9 ; Section 308 ! This is a ligitimate business
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Professional , Your email address has been submitted
to us indicating your interest in our letter . We will
comply with all removal requests ! This mail is being
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, Section 302 ! This is not a get rich scheme . Why
work for somebody else when you can become rich in
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Bức thư có vẻ là spam mail này chứa đựng một thông điệp bí ẩn và khơi mở cho tôi đến một lĩnh vực rất thú vị, đó là kĩ thuật che dấu thông tin, hay còn gọi là Steganography.

Tham khảo: http://en.wikipedia.org/wiki/Steganography

Sau vài giây Google, tôi tìm được một trang web trợ thủ đắc lực cho vụ này, tại http://www.spammimic.com/

Dùng chức năng Decode, chuỗi spam mail trên trở thành “I love you, Angel”

Funny huh?

PS. Để thử chính xác, hãy thử encode chuỗi “I love you…” thành spam mail và ngược lại.

Một ứng dụng rất hay khác, ẩn hình ảnh trong một bức tranh. Hãy xem hình sau:

1) Tranh phong cảnh

2) Khi lọai bỏ tất cả các bit ngòai 2 bit cuối cùng của giá trị R,G,B của từng pixel, kết quả sẽ là

(Tham khảo wikipedia)