There are a lot of things that can throw off flags for CC's. Theft is a big issue, and those card companies basically shoulder the burden of theft, so they take precautions to cut cards off if they think they are stolen. Things such as making a large number of purchases when you normally rarely use the card, having charges from geographically disparate locations in a short period of time (especially internationally), or a group of large transactions in a short time, etc, can set their flags off. I have had my bank call on 3 separate occasions to verify recent charges that they thought could be a sign of a stolen card. Each time they said if they hadn't been able to get me on my cell phone they would have frozen the card in hopes that I would then call in if the charges were legitimate.