🤖 Overview

MSIECrawler is a legitimate web crawler operated by Microsoft as part of its Bing search engine infrastructure, specifically serving the Microsoft Indexer Engine (MSIE) that powers Bing's web search index. According to Microsoft’s official documentation on Bing Webmaster Tools and the Bing Crawler Reference (available at https://www.bing.com/webmasters/help/which-crawlers-does-bing-use-8c184ec0), this bot is responsible for discovering and crawling publicly accessible web content to build and refresh Bing’s search results. It is one of several crawlers used by Bing, distinct from the Bingbot user-agent, and is often observed performing deep, comprehensive scans of websites.

🌐 Technical Behavior

MSIECrawler typically uses HTTP/1.1 and HTTP/2 protocols, sending requests with a User-Agent string of Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; WOW64; Trident/6.0; MSIECrawler) or variants like Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0; MSIECrawler). According to Bing’s own crawler identification page (https://www.bing.com/webmasters/help/verify-bingbot-16961a77), the crawler’s IP ranges are published in the Bingbot IP list which includes addresses from Microsoft’s ASN AS8075. The crawl pattern is aggressive, often sending requests at a rate of several per second per host, and it follows links recursively to discover new URLs. It respects robots.txt directives but may ignore noindex meta tags if the page is accessible via a crawled path.

📋 robots.txt Compliance

Based on Microsoft’s official guidance in the Bing Crawler Control Guide (https://www.bing.com/webmasters/help/controlling-crawler-behavior-1913340), MSIECrawler fully honors Disallow directives in robots.txt files. However, it does not support the Crawl-Delay directive—Bingbot and other Bing crawlers use their own rate-limiting algorithms instead. Evidence from real-world server logs confirms that robots.txt blocks are enforced; the bot will not visit disallowed paths after reading the file at the initial crawl.

🔍 Detection Indicators

The primary detection indicator is the User-Agent string which contains MSIECrawler and often a version of Internet Explorer’s Trident engine. Additional signals include a Referer header that may be absent or set to the root domain, and the IP address range belonging to Microsoft’s AS8075. The bot also sends a Accept header of text/html, application/xhtml+xml, */*. Log entries typically show a consistent, non-spoofed pattern with a user-agent that explicitly identifies itself as a Microsoft crawler.

📊 Data Usage

Data collected by MSIECrawler is used exclusively for Bing search indexing and to update web search results displayed to users. Microsoft states in its privacy policy (https://privacy.microsoft.com/en-us/privacystatement) that crawled content is stored temporarily to build the search index and is not used for AI training or targeted advertising. The bot does not extract personal data beyond publicly available text and metadata.

⚙️ Rate Limiting Policy

While MSIECrawler is legitimate, it is aggressive and can saturate server resources if left unconstrained. Rate limiting (e.g., blocking after 200 requests per minute per IP) is recommended to protect web server performance, as documented in Bing’s own crawling best practices (https://www.bing.com/webmasters/help/crawling-best-practices-92c24b9a). There is no official per-crawl delay, so threshold-based blocking is a standard defensive measure against excessive load.

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