how to mask credit card number (using regex?)

[eluser]Pygon[/eluser]
[quote author="Rick Jolly" date="1194053735"]
Well put untermensch. Coolfactor's question was very simple and clear, and it deserved an equally lucid, accurate answer. Like the internet in general, there is a lot of fluff floating around these forums.[/quote]

I see issues with literacy or reading comprehension abound; the question had been answered before any further discussion began.