You can read the report here: http://www.fincen.gov/statutes_regs/guidance/pdf/FIN-2013-G001.pdf Open the PDF in a VM if you don't trust it. Also, read through the discussion on the Bitcoin forum: https://bitcointalk.org/index.php?topic=154672.msg1639556 Basically, anyone trading more than $1000 worth of BTC a day will be regulated as a money transmitter or money services business (MT/MSB). For suspicious transactions, I think the same rules governing other financial transactions apply here as well. They look for more than just transactions over $10,000. All of those must be reported by law. However, they also look for patterns, but I don't know the details. They probably don't reveal the details on purpose, just as your bank uses secret algorithms to detect fraud and protect your account.