SAN FRANCISCO  Concerned by the wave of requests for customer data from law enforcement agencies, Google last year set up an online tool showing the frequency of these requests in various countries. In the first half of 2010, it counted more than 4,200 in the United States.

Google is not alone among Internet and telecommunications companies in feeling inundated with requests for information. Verizon told Congress in 2007 that it received some 90,000 such requests each year. And Facebook told Newsweek in 2009 that subpoenas and other orders were arriving at the company at a rate of 10 to 20 a day.

As Internet services  allowing people to store e-mails, photographs, spreadsheets and an untold number of private documents  have surged in popularity, they have become tempting targets for law enforcement. That phenomenon became apparent over the weekend when it surfaced that the Justice Department had sought the Twitter account activity of several people linked to WikiLeaks, the antisecrecy group.

Many Internet companies and consumer advocates say the main law governing communication privacy  enacted in 1986, before cellphone and e-mail use was widespread, and before social networking was even conceived  is outdated, affording more protection to letters in a file cabinet than e-mail on a server.