Banking fraud is an unfortunate fact of life these days. At some point when reviewing your monthly checking account statement or online activity, you may notice a purchase you didn’t make. What should you do next?

If you find any unauthorized transactions have occurred in your checking account, it’s important to handle the situation right away. When fraud involves a debit card rather than a credit card, the process can be a bit different.

There are a number of ways criminals can get their hands on your checking account information. It’s possible that you lost your card and the wrong person found it. Criminals also set up card skimmers and hidden cameras to steal your account number and PIN at places like ATMs and gas pumps. Sometimes, however, account holders accidentally give their personal information away.

“Social engineering is one of the most effective ways to gain access to a bank account,” says Jason Ioannides, manager of solutions consulting at Alloy, a financial technology firm that helps banks automate customer verification and identification. According to Ioannides, this is when a bad actor reaches out to a prospective victim and appears to be an authority figure.

After gaining some trust, the criminal asks “identity questions” to supposedly verify the victim’s identity before proceeding with some account action. Then, the thief uses the victim’s information – such as account number, Social Security number or mother’s maiden name – to answer security questions and access the victim’s account.

“If you discover a fraudulent charge, you should contact the bank immediately and speak to its fraud department,” Ioannides says. A representative will walk you through the next steps, such as canceling your debit card, ordering a new card and setting new online banking passwords. In some cases, your account will be frozen and require additional verification from you before any transactions can go through.

It’s also a good idea to follow up your phone call with a written or emailed letter. The letter should include your account number, the date and time when you noticed your card was missing or compromised, and when you reported the unauthorized transaction.

“Doing this quickly can mean the difference between a small loss and a big one,” Ioannides says. For one, if you report that your card was lost or stolen before any fraudulent transactions actually occur, you’re responsible for $0 in unauthorized charges, according to federal law. If you report a fraudulent charge within two days, you can’t be held responsible for more than $50 in charges. Keep in mind that you have 60 days to dispute the transaction or else you could be stuck paying for it. This works differently from credit cards, where most issuers offer zero liability on disputed transactions.

Once you dispute an unauthorized transaction, the bank has 10 days to investigate. If the transaction involved a merchant, it’s also a good idea to contact the merchant and dispute the purchase. The merchant may refund your purchase if the bank doesn’t.

When contacting your bank, you should call the number on the back of your ATM card. Ioannides warns that fraudsters are known to set up fake support numbers to get account holder information. If a bank apparently calls to alert you of a fraud attempt and is seeking personal information, hang up and call the number on the card rather than giving any information over the phone, as this could also be a fraud attempt.

Also, don’t forget that if you have bills set to autopay from your checking account, you’ll need to update your debit card number on those accounts. Failing to do so could result in late payment fees.

Here are some steps you can take to protect yourself:

Watch out for phishing. Be on alert for fraudulent emails, phone calls or texts that impersonate service providers such as banks asking you to confirm or provide personal or account information. “Financial institutions will not ask for confidential information – such as your name, password, PIN or other account information – when they reach out to you,” says a representative from Chase Bank.

Use caution at ATMs. If you’re using your physical debit card, be wary of where you swipe it. Criminals will often set up skimming devices at ATMs and other payment terminals that are isolated or otherwise hidden away.

Use technology to your advantage. According to Chase, your bank’s mobile app can help keep you safe when shopping, with features such as mobile alerts and the ability to lock and unlock your debit card. If you’re worried about unauthorized transactions, you can keep your card locked when you’re not using it and get alerted when certain types of transactions occur.

Set up extra security. A strong password for your online bank account isn’t enough these days. “Multifactor authentication and biometrics are great security mechanisms that many smart devices give us access to,” Ioannides says. It’s also a good idea to stick to a credit card instead of your debit card when shopping online since the fraud protection is more robust.

Keep an eye on your account. Since time is of the essence when it comes to catching unauthorized transactions, it’s important to regularly review your bank statements or online banking transactions. Doing so will ensure you catch questionable charges right away.