More lawyers and support staff are returning back to the office for the first time in over a year. But when they return, they may bring with them hidden malware if proactive measures weren’t previously implemented and followed, law firm cybersecurity experts said.

“The situation would be around them bringing in personal devices,” said David Wong, vice president of consulting at cybersecurity provider FireEye Inc. “If they bring in their personal devices and plug them into networks, if their system potentially has malware, they can possibly transmit [it].”