The web beacon tags are apparently able to collect information about an end user of a document and relay that information back to the beacon’s creator without being detected. Per WikiLeaks’ press release:
Today, April 28th 2017, WikiLeaks publishes the documentation and source code for CIA’s “Scribbles” project, a document-watermarking preprocessing system to embed “Web beacon”-style tags into documents that are likely to be copied by Insiders, Whistleblowers, Journalists or others. The released version (v1.0 RC1) is dated March, 1st 2016 and classified SECRET//ORCON/NOFORN until 2066.
Scribbles is intended for off-line preprocessing of Microsoft Office documents. For reasons of operational security the user guide demands that “[t]he Scribbles executable, parameter files, receipts and log files should not be installed on a target machine, nor left in a location where it might be collected by an adversary.”
