The government’s proposal to make Google share its search data with competitors would “deeply undermine user trust” by putting queries in the hands of potentially less secure rivals, the company’s search chief Elizabeth Reid testified Tuesday.

The Justice Department has proposed forcing Google to syndicate its ranking signals and other search data to competitors, something it says will level the playing field and end Google’s search monopoly. But Reid argued that exporting that data would shake users’ faith that their searches would stay private, and its value would create an incentive for hackers to go after small competitors. “Once it’s turned over to a qualified competitor, there’s no further protections we can give,” she said. “A startup is generally not a target because it’s small, but now it has this huge treasure trove of data.”

Google is fighting the DOJ’s sweeping proposals, which also include forcing it to sell its Chrome browser, by arguing for more limited changes to its search distribution contracts (it plans to appeal the monopoly ruling, but can’t do so until Judge Amit Mehta issues a remedies decision). Reid’s testimony follows that of other executives, including CEO Sundar Pichai, who claimed the government’s proposals could drastically change Google and the larger web. The DOJ says its proposals are all necessary to restore competition to the search market, and it’s argued that Google is exaggerating their dire effects.

Turning over information that powers Google’s search would not only make its competitors targets for hacks, Reid said, but it could undermine trust in Google’s products and search more broadly. Today, many people turn to Google to ask questions they may not even feel comfortable asking a friend, she said. “If suddenly they’re worried that data might go somewhere else … maybe they decide to not use Google altogether, [or] maybe they decide they’re not going to search for certain categories.” During its case-in-chief, by contrast, the DOJ brought in a privacy expert who testified search information could be safely shared with certain protections in place.

Reid echoed testimony from Pichai last week that the government’s data-sharing proposals could help rivals or spammers “reverse engineer” its systems, making it easier for them to get spam or misinformation ranked in Google results. Fighting these bad actors is “always a cat and mouse game, but it suddenly becomes a cat and mouse game where your hands are really tied behind your back,” she said.

Building the tools needed to follow the government’s proposals would divert engineering talent toward tedious compliance work instead of innovation, Reid continued. She testified that more than 20 percent of the search engineering force would need to focus on compliance “because it’s so extensive and invasive.” Even incremental changes to small features could trigger extra steps, so Google would likely shift its focus to areas “less covered by the remedies because that’s where we can stand out,” she said, though she didn’t get into specifics.

On top of all of this, Reid said maintaining the tools needed to distribute all the information the DOJ wants it to share with rivals would slow down its ability to ship features that improve users’ search experiences. “It’s just an incredibly large amount of work because these modules are constantly changing,” Reid said. “The business value of syndication versus the cost just doesn’t work out.”