Collection / Filtering

Suggest Good Practice


Once a warrant has been authorized or approved, an intelligence agency can proceed with the implementation of a particular surveillance measure. For this, it intercepts the relevant signals, for example by tapping an internet service provider’s (ISP) fiber optic backbone cable or diverting data at an internet exchange point. Afterwards, the collected data has to be filtered for two reasons: First, because of the huge volumes passing through, which would be far too much to be stored long term, gratuitous data that is extremely unlikely to yield any intelligence value is filtered out (e.g., all data from public video feeds); second, the collected data stream has to be filtered so as to abide by legal requirements. Certain data – for example the communications involving lawyers, journalists, priests, or other professions relying on the confidentiality of correspondence – may be offered higher levels of protection in national surveillance laws.


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Nerd Corner

Extract from the BND ruling on filters: “The service is to be obliged to continuously develop the filtering methods and to keep them at the state of the art of science and technology.” German Federal Constitutional Court, BND Law Judgment of May 2020, 1 BvR 2835/17, Paragraph 173.

CCC paper on technical capabilities of filters: Kay Rechthien. 2016. ”Sachverständigen-Gutachten gemäß Beweisbeschluss, 1. Untersuchungsausschuss (NSA-UA) der 18. Wahlperiode des Deutschen Bundestages.” September.

CTIVD report on the application of filters in “research assignment oriented” (OOG) interceptions by the Dutch intelligence services AIVD and MIVD (our translation), which is available in Dutch via the Review Committee on the Intelligence and Security Services: “Progress Report,” July 17, 2019 (CTIVD Nr. 63).

For a detailed analysis of potential applications for direct oversight access to operational surveillance systems, see: Kilian Vieth and Thorsten Wetzling. 2019. “Data-driven Intelligence Oversight: Recommendations for a System Update.”

Electronic Frontier Foundation. 2013. “Yahoo’s Challenge to the Protect America Act in the Foreign Intelligence Court of Review.” October 22, 2013. Other, more recent provider challenges include: Kate Conger. 2017. “An Unknown Tech Company Tried (and Failed) to Stop the NSA’s Warrantless Spying.” Gizmodo. June 14, 2017.

Privacy and Civil Liberties Oversight Board (PCLOB). 2014. “Report on the Surveillance Program Operated Pursuant to Section 702 of the Foreign Intelligence Surveillance Act.” July 2, 2014.