ORLANDO, Fla. -- Eyewitness News has learned that millions of debit and credit cards at SunTrust and several other major banks are at risk.

The card information was somehow compromised while in the hands of a third party vendor. Banks are sending their customers letters from SunTrust, Bank of America and Fifth Third bank.

---

DOCUMENT: Letter To SunTrust Customers

---

It all goes back to a 2008 breach of Heartland Payment Systems, a third party card processor, that suffered what's being called one of the largest data breaches ever.

Around the summer of 2008, hackers attacked Heartland Payment Systems out of New Jersey. The company processes 100 million credit and debit card transactions a month for restaurants, retailers and other merchants.

During the attack, thieves siphoned card data by installing software that watched for and recorded data as it was sent unencrypted over the company's internal processing networks.

Heartland estimates tens of millions of card transactions were stolen. When Visa and MasterCard found out, they alerted numerous banks, including SunTrust.

In turn, those banks sent a letter to customers who were affected. SunTrust won't say how many accounts were affected, but the letter informs SunTrust customers their check or credit card info, contained on the magnetic strip of their cards could have been stolen by hackers and that a new card with a new number will be issued.

Meanwhile, Heartland's website is advising cardholders go a step further by checking their records and to look for suspicious charges from telemarketers, inaccurate charges by retailers or any charge a customer is not confident was authorized.

If your card was compromised, you'll need to contact any business that automatically deducts payments from your card, like your gym or insurance company and give them the new card number.