May 19, 2014 – Do you use credit cards for personal purchases? If so, you should have at least two cards — one for purchases made online or by telephone and a second card for everything else.
This advice comes from the Postal Service’s Corporate Information Security Office (CISO), which points out the risk of a credit card being compromised is greater for online and telephone transactions. Using a separate credit card with a lower credit limit for these transactions reduces your exposure to potential fraud. 
Credit cards designated for online and telephone transactions are helpful because:
They aren’t tied directly to your bank account.
If the card is compromised, the impact to your daily routine is reduced while waiting for a replacement card.
It’s easier to track online and telephone purchases.
CISO said the advisory doesn’t apply to official business or travel-related purchases with USPS credit cards.
Source: USPS