Crooks have stolen more than $150,000 from a US business after embedding malware into an e-mail replying to an online job posting.
The FBI is warning small firms about the scam, which sees computers infected by malware contained in attachments to e-mails sent in response to job ads on employment Web sites.
In one recent case, the malware, which is connected to the infamous Zeus Trojan, enabled crooks to obtain the online banking credentials of a staff member.
The attackers changed the account settings to allow the sending of wire transfers, one to the Ukraine and two to domestic accounts, worth around $150,000.
The Bureau is advising companies to run virus scams before opening e-mail attachments and use separate computer systems for financial transactions.