What tipped off the credit card company for fraud? | Ask MetaFilter

What tipped off the credit card company for fraud? | Ask MetaFilter: "So here's a TLDR answer to your question:
When you use that card you're being watched. Sometimes by a person, but most often by computers that analyze and store every purchase you make. Even if you don't know it you have a data trail, and that data trail has a signature to it. When something breaks that signature, and is surrounded by other suspicious details, it either get automatically handled by a computer, and will eventually be handled by a human. The testing charge was suspicious, but maybe by itself wouldn't have mattered. Followed by tools (easy to fence, so a pretty common flag charge) it's no question. Especially if it looked at your account and couldn't find strong previous history with either. So your account gets sent to a high priority queue, and some underpaid dude on the eastern seaboard looks at it, tags it as fraud, and calls you to confirm, maybe helping him make an extra 200 bones at the end of the month."