Google is to blame for publishing a six-year-old news story that caused the stock of UAL, the parent company of United Airlines, to drop sharply on Monday, the Tribune said in a statement.

The problem started when Googlebot, the software program that Google News uses to index news sites, mistook one of the most popular stories on the Web site of The Sun-Sentinel, of Fort Lauderdale, Florida, for breaking news. The story, "United Airlines Files for Bankruptcy," was then posted on Google News as a new story, even though the original news story was published on Dec. 10, 2002.

"Google provided a link to the old story on Google News and dated it September 6, 2008. Google's dating the story on Google News made it appear current to Google News users," Tribune said in a statement.

The appearance of the bankruptcy story on Google News was blamed for a steep drop in UAL's stock price, leading the airline to issue a clarification.

"Reports that the company filed for bankruptcy are completely untrue and were caused by the irresponsible posting of a six-year-old Chicago Tribune article by the Florida Sun Sentinel newspaper Web site with the date changed," the airline said, noting it exited bankruptcy in 2006.

But the Tribune, which publishes several major U.S. papers, including The Chicago Tribune and The Los Angeles Times, said Google was responsible.

"On September 7, at 1:36:03 ET ... a user of the Sun Sentinel's Web site, viewing a story about airline policies regarding cancelled flights, clicked on the link to the old story under the 'Popular Stories Business: Most Viewed' tab. Fifty-two seconds later, at 1:36:57 ET ... Googlebot visited the Sun Sentinel's Web site again and crawled the story," Tribune said.

"This time, despite the fact that the URL to the old story hadn't changed, despite the fact that Googlebot had seen this story previously, it was apparently treated as though it was breaking news," it said.

Tribune said it asked Google "months ago" to stop using Googlebot to crawl its Web sites after it identified problems with the program. But Google denied such a request was ever made.

"The claim that the Tribune Company asked Google to stop crawling its newspaper Web sites is untrue," it said.

However, Google did not dispute that Googlebot misclassified an old story as breaking news. In a lengthy blog post, the search company said the story was indexed by Googlebot and appeared on Google News because it appeared in a list of popular business stories on the site, not because it was listed as breaking news.