A group of cyber-criminals have been hacking into the emails of publicly traded health care and pharmaceutical companies for over a year now. Their activities are detailed in a report released this morning by FireEye, a security research company in Silicon Valley.

The majority of the victims are top-level executives who are fooled by emails sent by client accounts, says Nicole Perlroth, who has written about the hacks in the New York Times.

The hackers are not deploying malware or anything that could potentially alert an anti-virus product, instead they’re essentially going through the email accounts in search of company information that can affect the stock market.

“According to the security researchers that first discovered these hackers, they think that they’re former I-bankers or at least have worked in the investment banking industry themselves,” Perlroth says.