I tend to check my credit-card account online every other day. It takes but an extra minute or two, and I can review all recently posted transactions to make sure all is in order.
This morning, I log on and see six charges made at 7-Elevens in Allentown, and Reading , PA. Now I don't think I've ever been to Allentown or Reading. Nor has my card left my possession. I get on the horn, they read through all recent transactions to make sure they others are all legit. The card is now canceled; I'll get a new one next week, and will have a few forms to fill out declining these unauthorized charges, which will then be refunded.
So, monitor your credit-card activity regularly!