WEB TECHNOLOGY — Understanding a “spider” (web crawler) In the context of Internet search and indexing, what is a “spider” and what does it do for the World Wide Web?

Introduction / Context:The term “spider” (also called web crawler or robot) is fundamental to how search engines discover, read, and organize pages. Knowing what a spider does explains why pages appear in search results and how website changes are detected over time.

Given Data / Assumptions:

• The question concerns Internet technology and search engines.
• “Spider” refers to automated software, not a human operator or a virus.
• Goal is to identify the correct functional role of a spider.

Concept / Approach:A spider systematically fetches webpages, follows hyperlinks, and sends content to an indexer. The indexer extracts words, metadata, links, and signals (titles, headings) to build a searchable catalog. Spiders obey rules placed in robots.txt and meta directives to respect crawling limits.

Step-by-Step Solution:Identify the domain: search/indexing technology.Recall definition: a spider is an automated crawler that discovers and downloads webpages.Match to option describing “program that catalogs websites.”

Verification / Alternative check:Search engines publicly document their crawlers (for example, user-agent strings) and how robots.txt controls their behavior. This confirms the spider’s role as a discovery and cataloging tool.

Why Other Options Are Wrong:A computer virus — malware that infects systems; not the same as a crawler.A hacker — a human attacker, unrelated to automated indexing.An application for viewing websites — that is a web browser.A firewall — a network security control, not a discovery bot.

Common Pitfalls:Confusing “crawler” with “browser.” Browsers render pages for humans; spiders fetch pages for indexing. Also, spiders do not judge truth or quality on their own; ranking happens later in the search pipeline.

Final Answer:A program that catalogs websites