The San Francisco 49ers said the names and Social Security numbers of nearly 21,000 people were stolen in a breach of the NFL team's computer systems earlier this year.
The acknowledgement was made in a required data breach notification filed with the state of Maine. According to the filing, which references a notification made to consumers on Thursday, the breach occurred in February and was discovered in August. A total of 20,930 people were affected.
Social Security numbers are considered one of a person's most sensitive pieces of personal information. When they're compromised, it puts people at risk for identity theft, because the numbers can be used to open lines of credit.
In a Friday statement to the press, the team said it's begun alerting those affected by the breach and is offering them free credit monitoring and identity theft protection services.
In its notification to the state of Maine, the team specified that it would provide one year of those services through Experian.
The 49ers said they're also working with cybersecurity experts to shore up cyberdefenses and prevent future breaches.