B1ff is type of internet slang that was created in the early days of the Internet by groups who felt they were being watched by government officials or corporations. This was a major step towards full 1337 (Leet); however, they originally had different purposes. B1ff only changes words only enough so a program looking for certain words doesn't find them, whereas 1337 was created to prevent non-1337 humans from reading text.
During the early days of internet gaming, a new side of b1ff took a significant rise, when scripts edited the content of instant chat conversations. Today, however, most censoring scripts can compensate for the letter-number replacement. Thus, b1ff has mainly evolved into 1337, a more involved language which, although it does include letter-number replacement, also includes letter mixing (e.g. "pr0n"), similar-sound substitution (e.g. "h4xx" for "hack"), 'building' a letter from multiple characters (e.g. x from ><), and the invention of new words as a substitute for common words.
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