Popular search engine Google has the potential to gather more personal information than any other company in the world, according to an online privacy expert.

Allison Knight of the Electronic Privacy Information Center, a Washington, D.C.-based public interest research centre, said that if Google's acquisition of online advertising company DoubleClick is approved, there could be wide-ranging privacy implications.

"Right now they're not doing targeted advertising. But once they acquire DoubleClick, they'll have the capability not only to use the search data that right now they're saving -- they'll also have access to profiles that DoubleClick has been creating," Knight told CTV's Canada AM.

"Every time you go to a website that has a DoubleClick advertisement, there's a log created of that activity. And those two pieces combined would actually allow Google to have more detailed profile on you than any other company in the world."

Google's proposed US$3.1-billion purchase of online ad company DoubleClick was announced on April 13 after a bidding war with Microsoft.

DoubleClick allows customers to insert and track online ads, including search ads, a crucial revenue generator for Google.

The proposed deal is currently the subject of an antitrust investigation in the United States, however it has not been indicated if privacy concerns will be part of the inquiry.

The concerns raised by Knight come after a report from an online privacy watchdog that rated Google as the worst of all online companies on privacy issues.

Of utmost concern to Privacy International was Google's ability to cross-reference information from its search engine, email, maps and instant messaging applications.

London-based group Privacy International said the Mountain View, Calif.-based company had "comprehensive consumer surveillance and entrenched hostility to privacy.''

Knight said this was because of the company's inconsistency between theory and practice on privacy issues.

"Every time you search on Google, your search terms are saved. These are saved indefinitely," Knight told Canada AM.

"Even though Google, a few months ago, did change their privacy policy to say that they would be obscuring this data, after two years it still is saved indefinitely and the searches that you do online can reveal so much about your offline life," Knight told Canada AM.

While Knight did acknowledge that Google is not the only online company retaining user search data, she said it was the largest company involved in the practice.

Google has said that it stockpiles user data to improve search results and defended their record on user privacy.

"We are disappointed with Privacy International's report, which is based on numerous inaccuracies and misunderstandings about our services,'' Nicole Wong, Google's deputy general counsel told The Associated Press.

"It's a shame that Privacy International decided to publish its report before we had an opportunity to discuss our privacy practices with them.''

Privacy International contacted Google earlier this month, but didn't receive a response, Simon Davies told the Associated Press.

On Monday it was revealed Google filed a document with the U.S. Justice Department on April 18, alleging the latest version of Microsoft's Windows operating system impeded the effectiveness of desktop search programs.

With files from the Associated Press