"Even if you are not a criminal, you probably make searches that you don't want your minister, boss, or spouse to know about," said Blekko's Greg Lindahl.
Weinberg said DuckDuckGo's model allows it to make money through "keyword" advertising, without stored profiles. So if someone is searching for a "mortgage", they might see ads for banks.
This differs from search engines that track the pages people visit and then deliver related ads, a practice known as "retargeting".
"Retargeting is effective only for a small amount of people, the rest are just annoyed by it," he said.
Danny Sullivan, editor in chief at the specialised website Search Engine Land, said these kinds of search engines were "interesting" but unlikely to have a major market impact.
"It's extremely unlikely in the next three to five years that any player will come along and take a sizeable share away from Google," he said.
A survey of the US market by the research firm comScore showed Google with a 66.5 per cent market share, with 13.3 billion search queries in a month, followed by Microsoft (17.3 per cent, 3.5 billion) and Yahoo! (12 per cent, 2.4 billion).
Sullivan said the news over NSA surveillance "so far doesn't seem to be spooking" the public.
He said Google does not force people to create a profile that can be used to connect with its other services.
"You can go to Google, and you can do a search without being logged in, and you still get very good results," Sullivan said.
"If you do log in and connect to these services, Google blows DuckDuckGo out of the water. When it has access to your calendar and search history, Google can predict your answers before you even ask them."
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