if the words or components of a passphrase may be found in a language dictionary—especially one available as electronic input to a software program—the passphrase is rendered more vulnerable to dictionary attack. this is a particular issue if the entire phrase can be found in a book of quotations or phrase compilations. however, the required effort (in time and cost) can be made impracticably high if there are enough words in the passphrase and how randomly they are chosen and ordered in the passphrase. the number of combinations which would have to be tested under sufficient conditions make a dictionary attack so difficult as to be infeasible. these are difficult conditions to meet, and selecting at least one word that cannot be found in "any" dictionary significantly increases passphrase strength.