Square Security Via Sytist-data Breach?

I had a customer place an order via the Square integration on our website, as we have done for several years now.

She sent me an email stating that shortly after placing the order, she had 20 charges totally $500 almost immediately following placing that order.

Should we be concerned or was it possibly a coincidence?

Very unlikely. Sytist doesn't capture or store any credit card information except for the last 4 digits and the transaction ID. 

You are on an older version of Sytist and your support period is expired, but I am answering this any ways because it will get a lot of attention.

Sounds like their browser was hijacked or they have malware.