Apple said that it retains user mobile data from its Siri personal assistant for up to two years.

According to a report from Wired and the ACLU, the company said that it maintains information in an anonymised capacity and uses the data for development of the platform.

The report cited Apple spokespersons in explaining that while it retains the information, the company does not log user names or mobile numbers, opting instead to associate collected data with a random numerical token.

The company said that the information is kept on file in Apple datacentres for six months and is then disassociated with the identification number. The information is then housed for another 18 months for developer reference.

The storage and retention of user data has become a contentious issue, both in the public and private sectors. Social networking sites and web application providers in particular have found themselves facing criticism for the retention of user data.

The issue came to a head in 2010 when Google was found to be collecting data from public wi-fi networks with its Street View imaging vehicles. Earlier this week the company was slapped with a fine from German authorities over the practice.

Last year, the UK government triggered debate when it unveiled a controversial new set of data retention laws. Critics argued that the laws will allow government agencies to further pry into the personal lives of citizens.