The US Treasury department revamped its policies for participating in bond auctions in 2009, after finding that China was buying more in US government debt than was being disclosed, Reuters reported. At the time, Washington said the change was simply to modernize procedures. However, a Reuters investigation has found that the real reason was that China was potentially violating bond auction rules using a method, known as “guaranteed bidding”, to buy Treasuries that effectively hid billions of dollars of purchases in each auction. Treasury officials have worked to keep the reason for the auction-rule change under wraps, and staff were told not to mention any specific creditor’s role in the matter. Chinese entities hold at least US$1.15 trillion in US government debt, accounting for roughly 26% of debt issued by Washington.