Although such companies try to keep their users' information private, their business models depend on exploiting it to sell targeted advertising, and when governments demand they hand it over, they have little choice but to comply.
Suggestions that BlackBerry maker RIM might give user data to British police after its messenger service was used to coordinate riots this summer caused outrage -- as has the spying on social media users by more oppressive governments.
But the vast amount of personal information that companies like Google collect to run their businesses has become simply too valuable for police and governments to ignore, delegates to the Internet Governance Forum in Nairobi said.
"When the possibility exists for information to be obtained that wasn't possible before, it's entirely understandable that law enforcement is interested," Google's Chief Internet Evangelist Vint Cerf told Reuters in an interview.
"Then the issue would be, what's the right policy? And that, or course, engenders a lot of debate," said Cerf, who is recognized as one of the "fathers of the Internet" for his early work in areas including communications protocols and email.
Demands from governments for Internet companies to hand over user information have become routine, according to online privacy researcher and activist Christopher Soghoian, who makes extensive use of freedom-of-information requests in his work.
"Every decent-sized U.S. telecoms and Internet company has a team that does nothing but respond to requests for information," Soghoian told Reuters in an interview.
Soghoian estimates that U.S. Internet and telecoms companies may receive about 300,000 such requests in connection with law enforcement each year -- but public information is scarce.
While U.S. courts are obliged to publish reports on wire-tapping of telephone lines, no similar information is required to be made public with respect to the Internet -- which grew up after the laws on electronic communications were passed.
Google does voluntarily publish a transparency report every six months in which it details the number of requests it receives from governments around the world to remove content from its services or hand over user data.
But the numbers do not reveal how many users are affected by each request -- only trends country by country (www.google.com/transparencyreport).
Some governments are requiring Internet companies to collect more data and keep it for longer, said Katarzyna Szymielewicz, executive director of Poland's Panoptykon Foundation, which campaigns for human rights in light of modern surveillance.
"Government agencies throughout the world are pushing companies to collect even more data than is needed for their business purposes," she told the conference.
"For example, we have a very controversial data retention regime which is currently under review. This requires people to store data for a period up to two years so it can easily be accessed by law enforcement agencies."
The ease and cost of surveillance are at an all-time low, Soghoian said, with Google charging an administrative fee of $25 to hand over data, Yahoo charging $20, and Microsoft and Facebook providing data for free.
"Now, one police officer from the comfort of their desk can track 20, 30, 50 people all through Web interfaces provided by mobile companies and cloud computing companies," he said.
"The marginal cost of surveilling one more person is now essentially approaching zero."
(Reporting by Georgina Prodhan; Editing by Will Waterman)