Perplexity Is Using Stealth Bots and Breaking Website Directives to Fetch Data, Says Cloudflare

Perplexity is said to be illegitimately accessing content from websites despite being prohibited from doing so. Cloudflare, a global web security services company, conducted a test to confirm the stealth behaviour of the answer engine company. The researchers highlighted that not only were crawler bots from Perplexity ignoring the directives from the websites, but they were also actively hiding their identity via multiple means to ensure website owners could not track the activity. Cloudflare was also able to find a way to successfully shut down the artificial intelligence (AI) company's efforts.

Cloudflare Catches Perplexity's Stealth Tactics in Action

In a blog post, the web security platform claimed that Perplexity was involved in “stealth crawling” activities. “We see continued evidence that Perplexity is repeatedly modifying their user agent and changing their source ASNs to hide their crawling activity, as well as ignoring — or sometimes failing even to fetch — robots.txt files,” the post added.

Before delving into Perplexity's behaviour, it is important to understand how the entire system works. Owners of content websites add information, and third-party services such as search engines fetch this data to index these websites and make them appear when a relevant query is typed. Some apps and websites also scrape websites to either surface them within their interface or collect data with permission.

However, for this relationship between websites and crawlers to work, there must be trust. It is established by these bots following a set of rules when crawling any website. These rules dictate that the activity of bots must be transparent, they should serve a clear purpose and perform only specific activity, and they should follow website directives and preferences. So, if a website blocks a bot, it should not crawl their website.

As per Cloudflare researchers, Perplexity is breaking this trust model by using stealth tactics to scrape website data even from those websites that explicitly block its declared bots — PerplexityBot and Perplexity-User. The researchers were able to confirm this activity by creating new test domains.

These domains were not indexed by any search engine or made publicly accessible or discoverable. Additionally, the researchers implemented a robots.txt file (a text file used by websites to give instructions to web crawlers) to stop all bots from accessing any part of the website.

Then, Cloudflare researchers went to Perplexity and asked it specific questions about these newly created domains. They found that, despite following Internet protocols to prevent crawling activity, Perplexity was still able to surface detailed information about these websites.

Cloudflare claims Perplexity's user agents or web crawlers take several steps to bypass websites' directives and access the data. If a declared user agent is denied access via robots.txt, it ignores it and continues to scrape data. If a website has implemented a web application firewall (WAF) to block the bot, the company uses a generic browser agent intended to impersonate Google Chrome or macOS.

This undeclared bot is also said to utilise multiple IPs not listed in Perplexity's official IP range to trick the website. To further hide its tracks, these crawlers were said to use different automatic system numbers. Notably, Cloudflare stated that when these undeclared bots were successfully stopped, the quality of Perplexity's responses declined, as it began to rely on other data sources to answer the query.

Cloudflare said its bot management system was able to register all the undeclared crawling activity from Perplexity's hidden user agents and is now automatically protecting all its bot management customers. Additionally, the company has added signature matches for the stealth crawler to its managed rule, which blocks AI crawling activity. This is available to all Cloudflare users, including those on the free tier.