A third-party site that relies on Craigslist data has accused the classified giant of changing its policies in an effort to kill it off. Craigslist has reportedly told major search engines to stop indexing its users' ads. That could leave 3taps, which operates the site Craiggers and re-publishes the data for use by third parties such as Padmapper to use, out in the cold.

"At approximately noon on Sunday August 5, Craigslist instructed all general search engines to stop indexing CL postings," says a statement on the 3taps homepage. Because 3taps had been harvesting Craigslist data from cached copies offered by Google and Bing, the move to block search engines means Craigslist is "effectively blocking 3taps and other third party use of that data from these public domain sources," 3taps claims.

"We are sorry that CL has chosen this course of action and are exploring options to restore service but may be down for an extended period of time unless we or CL change practices," the company says.

3taps seems slightly confused about when the block started. Its website states it began on Sunday, August 5, but the Verge noticed a tweet, published early Tuesday morning, that says Craigslist changed its policy on Monday. We've asked 3taps for clarification and will update when we have it.

The search engine block would be only the latest step Craigslist has taken to shut down competing services. Two weeks ago, the firm filed suit against 3taps and Padmapper, accusing them of copyright and trademark infringement. Last week, Craigslist beefed up its terms of service in an apparent effort to shore up what experts have told Ars is a flimsy legal case.

But the lawsuit would become all but irrelevant if Craigslist prevents third parties from crawling its site in the first place. That would also be a serious loss for users who prefer the more sophisticated interface of sites like Craiggers or Padmapper to Craigslist's "old and busted" look.

We've asked Craigslist for comment and will update the story if they respond.

Update: A couple of readers have pointed out that Craigslist has set the NOARCHIVE robots meta-tag, but not the NOINDEX tag. So Craigslist posts should still show up in search results, but 3taps will be deprived of the cached copies of those posts it was using to build its own database.