Which of the following is the most efficient search?

The choice involving the search query that specifies the index as "security" and includes the phrase "failed password" is considered the most efficient because it narrows down the scope of the search to a specific index known to contain relevant data. By targeting the "security" index directly, this search reduces the amount of data Splunk needs to sift through, which can lead to faster search results and lower resource consumption.

Selecting a specific index is significant because it helps in refining the query to only the most pertinent logs. In contrast, searching across all indexes or using broader index patterns can result in unnecessary processing of irrelevant data. This can slow down performance and lead to higher resource utilization.

The other choices illustrate less efficient approaches. Queries that search across all indexes (like in the first option) or utilize multiple indexes (as in the third option) may encounter a larger volume of data, increasing the time and computational power needed to return results. This inefficiency is compounded by the fact that the broader the search parameters, the more irrelevant results are likely to appear, requiring additional filtering by the user. Thus, specifying the "security" index in the recommended choice optimizes search efficiency while maintaining the focus on pertinent information related to "failed password."