Cullen heads up the privacy arm of Microsoft's Trustworthy Computing Group, which has led the company's drive to tackle security and privacy threats arising from its products. The specialist security group, headed up by ex-US federal prosecutor, Scott Charney, was established in 2002 as a response to heightened security concerns following the September 11 attacks.

Cullen said that Google had not invested enough to build privacy into its products, citing Street View, as a prime example.

"Microsoft has over 40 full-time people invested in privacy and over 400 part-time people. Google hasn't -- at least from what I read about them -- evolved to that," he said.

"We think about privacy as part of the core design... We have thought about how to design privacy into the product, as opposed to how to react to the negative impressions," he said.

Google's lead engineer for its Maps application Lars Rasmussen has previously brushed off criticisms of its approach to privacy. "So, these are all images that anyone could go out and take with a camera. We do take great care that if someone did feel their privacy was invaded, there is a way that they can easily tell us about it and we'll remove it right away," he said earlier this year.

Cullen expects Google to sharpen its approach to privacy in the future as Google's dominance of search advertising -- exactly where Microsoft would like to make its mark -- continues.

"The thing is, any time you get a provider in the market that has a predominantly large share of that market, questions start to get asked about their practices, about what their motives are," he said.

"I desperately hope that they ... in fact I expect that they will change. They will become as grown up as some of the larger companies around, so in some respects it's a predictable thing," added Cullen. -- Liam Tung, ZDNet.com.au.