How do they know?

[tinapbeana]

when i was going to be in argentina for a month for work, we called my bank and gave them advance notice and had no problems.

what we did have problems with was my LD company: they placed a block on my line after a week for possible fraud even though they also had advanced notice. the ironic part? the LD company was the company i worked for at the time and THEY were the ones that sent me to argentina! i put the appropriate international calling plan on my account personally and left full notes on the account regarding the situation and the necessary contact information if the fraud deparment needed to verify anything... oh well...

[greedy4chips]

For online purchases try using "1-time use" or "virtual credit card #s". Many credit card companies offer this now as a way to protect your credit card information from being stolen.

Read about it here Outsmart thieves with virtual card numbers

[Daylily]

That is really strange about the WalMart transaction. How would they know????
I've had one issue with fraudulent use. I always assumed that fraudulent use would have to be done over the internet or over the phone. Not so. The thieves actually made a card with my info on it. The credit card company called and asked if we had been to Las Vegas, El Paso and Mexico. There was a string of charges over a couple day period - and they were 'swiped' transactions. Someone actually had a card with my info.
We had our cards and hadn't had any mailed to us that we didn't receive.

[greedy4chips]

I am in the process of writing a computer program that uses a magnetic strip reader to read the encoded data on any card with a magnetic strip on it. For a mere $50 you can buy a reader and see exactly what is on any card. For another $450+ you can buy an encoder to encode blank cards which can be purchased for pennies and duplicate your card.

Imagine you hand your cc to a waiter or waitress and they have a card reader hidden somewhere and read your data. All they need then is exp date and cvs # and you are toast.