Costco's access denial stems from their DDoS protection and fraud prevention systems flagging your connection as non-human or risky. Their CDN and Web Application Firewall monitor traffic patterns in real time, and certain triggers get you blocked immediately. Common causes include using a VPN or proxy server that shares an IP with bot traffic, browsing from a datacenter IP range, sending too many requests in a short window (even manual rapid clicking can trigger this), or accessing from a country where Costco doesn't operate retail locations. Browser extensions that modify headers or block JavaScript can also trip their security rules. Corporate networks and public Wi-Fi sometimes share this problem because hundreds of users funnel through the same gateway IP. Costco runs a tighter security posture than most retailers because they handle membership data and payment information for 130 million cardholders. Their risk tolerance is low. They'd rather false-positive block a legitimate user temporarily than let automated scrapers pull pricing data or allow credential stuffing attacks. To fix it: disable your VPN and try from your home ISP connection, clear cookies and cache completely, switch browsers or use incognito mode, or wait 30-60 minutes if you triggered a rate limit. If you're on a shared network, you might need to contact Costco's support team to whitelist your IP, though they rarely do this for individual users. For agencies like Ottawa SEO running technical audits or competitor analysis, Costco's site is notoriously difficult to crawl programmatically. You need residential proxies with proper rate limiting, rotating user agents, and randomized timing between requests. Even then, expect blocks. Their IT team clearly prioritizes security over crawlability, which is a defensible tradeoff for a membership-based retailer with tight margins who doesn't rely on organic discovery traffic the way pure-play e-commerce sites do. Most of their customers arrive by typing the URL directly or using the app.