A further 6 percent were vaguely described as "national security."
While communications service providers can be ordered to retain data for up to 12 months in case it is needed in an investigation, 88 percent of the data requested was less than four months old -- and the vast majority of that a matter of days old.
About two-thirds of applications for surveillance approval were waved through; only about one in 12 were rejected, the rest being returned for further justification or clarification.
The necessity and proportionality of the surveillance were the most common reasons for rejecting or returning requests.
IOCCO's report also tracks warrants for interception of the content of calls and communications. It said 3,059 interception warrants were issued in 2015, a 9 percent increase on 2014. The number had remained stable between 2013 and 2014, after falling from 3,372 in 2012. One-third of the 2015 warrants was issued for reasons of national security, the rest for the prevention of serious crime, the proportion stable since 2014.
While the authorities' collection of metadata is short-term, almost impulsive, their listening activities are more systematic and long-term. The interception warrants have an initial duration of three or six months, and can be prolonged. Around half of the year's warrants were still in effect at year-end, and some interceptions had been going on for longer than a year, the report noted.
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