Google Inc. is shortening the life span of its “cookie” data-tracking file – but it’s not clear whether the move would do much to enhance privacy.

Under the new policy, the cookies would expire automatically after two years, instead of in 2038 as is currently the case. However, the two-year period could get automatically extended when users revisit Google’s search engine, so one might have to avoid Google for a full two years to see the cookie automatically expire.

“It sounds like it changes things … but the reality of how people use computers, I don’t think it in reality changes anything substantially,” said Pam Dixon, executive director of the World Privacy Forum, a nonprofit privacy-advocacy group.

Privacy advocates have become increasingly concerned about Google’s privacy practices as the company expands into services such as e-mail, maps and photos. Data retained by Google could be subpoenaed by law-enforcement agencies and other parties. Google already has decided to remove key pieces of identifying information from its system every 18 months to address those worries.