Parent Files Suit Against CoStar, Claiming Theft of Proprietary Information

Mere weeks after the and CEOs hurled hurled insults and accusations at each other as the residential real estate portal giants fight for second place behind Zillow, the battle was ratcheted up further on July 2 when parent Move, Inc. filed a lawsuit in the U.S. District Court in California, claiming that a former Move employee now working for parent CoStar Group stole proprietary information helping expand its burgeoning business.

Move, owned by the Rupert Murdoch-led media company News Corp, wrote in its complaint that James Kaminsky, “a former Move employee now working for Move’s direct competitor, CoStar, systematically invaded Move’s secure computer systems, secretly exfiltrated Move’s trade secrets, and spied on Move’s real-time confidential electronic documents to give CoStar a massive unfair competitive advantage and to help CoStar increase traffic to its competing real estate listing website, all to the detriment of Move.

“There is nothing wrong with lawful – even intense – competition. But competitors should never be allowed to cheat and steal to get ahead.”

Move is requesting a jury trial and damages.

In an emailed statement to RISMedia, Co-Star scoffed at the charges and vowed to fight them in court.

“This lawsuit is’s latest desperate attempt to distract from the fact that has replaced as the number two portal according to the parties’ own site-centric data gathering tools,” wrote Gene Boxer, general counsel. 

“The employee in question is a mid-level manager who writes and edits stories about condos. Safe to say he has zero input into’s strategy. And even Move’s creative writing exercise doesn’t pretend that CoStar itself engaged in any misconduct. This is a PR stunt that is already backfiring. is losing the battle with and its attempt to change the story doesn’t change that reality. We look forward to prevailing in court.”

The claim made specific allegations about how Kaminsky assisted and illegally hurt

“ has succeeded in building up significant website traffic, and it uses various marketing strategies to increase and maintain that traffic, including traditional advertising on television and across the Internet. also relies on a strong, established and successful “News & Insights” platform as part of its product offering and to attract real estate professionals, consumers and other visitors to The platform is featured prominently on the website. 

“The News & Insights team publishes quality content, working with groups across the business and with others in the media to report and comment on real estate and related topics. News & Insights is key to building Move’s and’s brand awareness, goodwill and loyalty. 

“CoStar apparently wants to create a rival News & Insights platform for, copying the success of the News & Insights team at CoStar recently hired the former head of’s News & Insights group, Defendant James Kaminsky. For nearly a decade, Mr. Kaminsky led’s News & Insights group, with knowledge of nearly every facet of the business, including strategy, organizational structure and operational details. He has referred  to the News & Insights group at as ‘an essential branding and monetization engine for’

“Now at CoStar, Mr. Kaminsky is managing a team of writers, just as he did at He holds himself out as a “Content Strategist,” “Senior Editorial Director,” “Team Leader,” and “Brand Builder.” According to his LinkedIn profile, Mr. Kaminsky’s new employer is “CoStar,” and his new title is “Editor,” Mr. Kaminsky now manages and supervises a team of 10 other employees at CoStar working to build up a new digital product similar to’s News & Insights platform.

“In June 2024, Move discovered that CoStar, through its employee, Mr. Kaminsky, has been brazenly and repeatedly misappropriating Move’s confidential and trade secret information to give a massive jump start in setting up its new offering. As he departed Move, Mr. Kaminsky stole confidential business information, sending it to his personal email account on the last day he had access to Move’s computer system. He established surreptitious, undetected ongoing access to allow himself (and, thus, CoStar) to spy on Move’s highly confidential documents  stored on protected computer systems. 

“Then, attempting to cover his tracks, Mr. Kaminsky deleted nearly a thousand files from his Move computer and wiped clean his entire browsing history before returning the device to Move. Since he left Move, for several months including a significant period of time in which he was with CoStar, until he was recently caught red-handed, Mr. Kaminsky unlawfully exploited ongoing access to Move’s confidential and trade secret information which was being updated by unsuspecting Move personnel in real-time.”

This story will be updated as new details emerge. To view the full filing, click here.

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