[4]: 59 [5]: 149 [6]: 384 [3][7][8][9][10] The software uses time-controlled web spiders to avoid detection, and likely countermeasures, by the webmasters of the targeted site.
Use of Xenon was begun in the Netherlands in 2004, by the Dutch tax authority Belastingdienst.
The Amsterdam-based data mining firm Sentient Machine Research, together with the tax authorities of Austria, Canada, Denmark, and the United Kingdom, has since upgraded the system.
[3] Swedish privacy advocate and IT expert Par Strom, while stating in 2007 that the anticipated use of Xenon by the Swedish tax authority Skatteverket would be legal, has also stated that such use would pose dangers to citizen privacy rights—as did the current use at the time of similar spidering software developed internally by the Swedish government.
[1] Canadian Internet law expert Michael Geist has expressed similar privacy concerns.