In some password-authenticated sites, you are asked to enter a random selection of specific characters from your password rather than the whole word/phrase. For example, it might say 'Enter the 1st, 4th and 8th letter' and provide three separate input boxes.
From what little I know of security mechanisms, I would have expected this to be less secure than entering the whole password, salting + hashing it and comparing it to the stored hash, as there is no plain text anywhere in sight.
This system is used by (hopefully) very secure websites, though, including certain bank sites in the UK.
So my two-part question is, is this as secure as traditional salt/hash comparison and why is it so?