After days without phones and email following a cyberattack across Europe, DLA Piper's U.S. operation is back up and running.

The malicious software that caused the outage, called Petya, is thought to have originated in tax software used by companies and accountants in Ukraine. Once on a computer, the virus locked users out of that device's data and asked for a $300 ransom payment.

The software update carrying the virus came on June 27—in the middle of the night for the United States—and spread through computers across DLA Piper's network. The bug may not have reached as many firm computers stateside, since not all would have been connected online outside work hours. But email and phone service at the firm appeared to be down across the firm's U.S. offices until Friday.