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A comment on When Undercover Credit Card Buys Go Bad. Parent comment

Re:When Undercover Credit Card Buys Go Bad by bkruse on Tuesday December 08, 2015 @10:43AM (#10696987)
Bloomberg does this with data sales. They'll sell you particular financial information, like tick-by-tick for the Russell 2000 over the last 5 years. They embed unique hidden markers or fake trades with everyone they sell them to. They then go and acquire data from other "providers", and find the leak.
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Re:When Undercover Credit Card Buys Go Bad by alasdair_ on Tuesday December 08, 2015 @03:19PM (#10699156)
Can't people just make two independent purchases of the data and diff them to find the issues?
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Re:When Undercover Credit Card Buys Go Bad by brokentone on Tuesday December 08, 2015 @11:10AM (#10697214)
Would fake trades not be distorting the data you are purchasing from them?
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Re:When Undercover Credit Card Buys Go Bad by bkruse on Tuesday December 08, 2015 @12:21PM (#10697810)
From what I understand, they used to change volume slightly which they claim wouldn't negatively impact algorithms looking at historical data. Then, however, people were using volume weighted average pricing (VWAP), which would eliminate that change. This is just theory now, but I believe they just add double trades, instead of fake trades are certain prices.
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