SAN FRANCISCO - Google Inc. and Apple Inc. also collect location data from computers, according to new reports in the US media Tuesday amid privacy concerns over the technology giants tracking mobile phone users.

The two companies obtained the information after a computer scans the area around itself for available Wi-Fi wireless networks, typically after users give a website permission to determine the computer's approximate location, The Wall Street Journal said in a report on its website.

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Google is believed to gather the location data through software in its Chrome browser or search toolbar. The same software can also be found in other browsers, such as Microsoft Corp's Internet Explorer and Mozilla Corp's Firefox.

When users explicitly agree to let certain websites find their location, their computers will scan for nearby available Wi-Fi networks, and then the Google browser or toolbar will send the information back to Google's location database.

Apple's method of gathering location information was disclosed in a letter last year from its executives to the US federal lawmakers, The Wall Street Journal said.

According to the letter, some Apple Macintosh computers send location information to Apple if the computers are connected to the Internet through Wi-Fi networks and are using location-based services, such as those automatically identifying the local time zone.

In its letter, Apple said it also obtained location data when users surfing the Web with Apple's Safari 5 browser allowed an application, such as Google Maps, to find the computer's location.

The data is "collected anonymously, and is stored in a database accessible only by Apple," the letter said.

The computer-location data were used by Google and Apple to build highly precise databases of Wi-Fi networks, improve users' experience or target more-relevant ads to certain users, The Wall Street Journal said.

But it noted that it was not known whether Apple used the data it collected for other purposes or whether it had made any changes recently in its tracking functions.

Last Friday, media reported that security analysts had found Apple's iPhone and smartphones running Google's Android operating system regularly transmit users' locations back to the two companies.

Moreover, it is said iPhone was collecting and storing user location data even when location services were turned off.

The news of location tracking by information technology giants has aroused public concerns about their privacy being violated. Some countries have launched probes into Apple and other developers.