Final answer:
Salting password hashes involves adding a unique, random string to each password before hashing, which nullifies the effectiveness of precomputed rainbow tables used in cracking password hashes.
Step-by-step explanation:
The question pertains to computer security, specifically how 'salting' password hashes can counteract the effectiveness of rainbow tables, which are precomputed tables used for cracking password hashes.
When a salt, which is a random string of characters, is added to a password before it's hashed, the resulting hash becomes unique, even if the original password is not. Consequently, the use of salt necessitates that a new rainbow table be generated for each unique salt.
This process renders precomputed rainbow tables essentially useless because each password hash has its own unique salt, thus requiring an impractically large number of tables to be effective in an attack.