Shares in video game retailer GameStop dropped about 1% this afternoon after it confirmed to website KrebsOnSecurity.com that it’s investigating a possible hack from someone who took payment card data and then, it says, “offered [it] for sale on a website.”

GameStop says it learned about the possible breach from “a third party.” It has engaged “a leading security firm” to investigate. Meanwhile it will “continue to work non-stop to address this report and take appropriate measures to eradicate any issue that may be identified.”

The Texas-based company urged customers to check their payment card receipts for unauthorized charges. Those who find one should “report it immediately to the bank that issued the card because payment card network rules generally state that cardholders are not responsible for unauthorized charges that are timely reported.”

The report comes at a difficult time for GameStop: Its stock price has depreciated 25.6% over the last 12 months and last month said it plans to close about 150 stores.

CEO Paul Raines told analysts last month that 2016 was “a more difficult year than we originally forecast” with sales of physical games down 15% as the console business matures. It projects same store sales this year to be flat or down as much as 5%,

The company is diversifying, and hopes to have half of its earnings come from other sources by 2020.