Phishers are sending out fake messages from the Federal Trade Commission that drop malware onto the machines of users who click the malicious attachment.

In response, the FTC has issued a public warning to consumers not to open fraudulent emails made to look as though they come from its fraud department. The email says it’s from “frauddep@ftc.gov” and has the FTC seal. Click on the attachment and you’ll download malware designed to steal passwords and account numbers, the agency warned.

“It’s a treasure trove for identity theft,” David Torok of the FTC’s Bureau of Consumer Protection told the Reuters news service. “We’re concerned. The virus that’s attached to the email is particularly virulent.”

The agency doesn’t know how many people found the email in their inboxes, but Torok confirmed the agency has received hundreds if not thousands of calls and complaints.

Recipients of the email are advised to forward it to spam@uce.gov, an FTC spam database used in its online fraud investigations.