The Fidelity data breach exposed the personal data of 77,000 customers

Fidelity Investments suffered a data breach that compromised the personal information of 77,000 customers, the company said in a notice to the Maine attorney general's office on Wednesday.

The breach occurred in August and is linked to two accounts recently opened with the wealth management firm, according to the filing. It's not clear how these accounts allowed hackers to access customer data.

Fidelity did not disclose which specific customer data was accessed by the thieves, but said after completing its investigation that no customer accounts or funds were compromised in the breach.

“We detected this activity on August 19 and took immediate action to shut down access,” Fidelity said in a notification letter to customers.

Fidelity declined to provide further comment on the breach, but told CNET in an email that it has resources available to assist customers with questions about the attack.

“Fidelity takes customer service and protecting information seriously,” the company said.

Read more: The data breach exposed the Social Security numbers of 237,000 Comcast customers

What to do if you are involved in a fiduciary breach?

The Fidelity data breach affected a small percentage of the company's 51.5 million customers. If you're affected, Fidelity is offering 24 months of credit monitoring and identity theft protection services from TransUnion Interactive. To activate this offer, use the code provided in your letter sent via USPS mail. Identity theft protection can help notify you in advance of a data breach and alert you if your personal data is available on the dark web.

In addition to taking advantage of this free service, you should change your password and monitor your Fidelity account for any suspicious activity. If you have a Fidelity account and aren't sure if you've been affected, it's always a good idea to change your password. Updating your password regularly can make it harder for bad actors to hack your account. A password manager can make that process much easier.

Depending on what sensitive data you have accessed, you should monitor your credit reports with TransUnion, Equifax and Experian.

You can even decide to place a fraud alert on your credit or freeze your credit with each of the three credit bureaus so that no one can open new credit accounts — such as car loans or credit cards — in your name.