The finance department of a New Jersey County has had a lucky escape after criminals hacked its online bank account, stealing only $19,000 (£12,000) from an account that held millions.

The theft from Salem County occurred in December after malware believed to be the Zeus banking Trojan nabbed the logins for the Microsoft Exchange system connected to the administration of the account.

The sum of $19,380.70 was transferred from the County’s account ay Fulton bank to an external account at JP Morgan Chase in California, locking out the County's officials from the main account for a period of time.

Given that the account held £13 million in funds, the theft could have been much worse, County officials told local news media.

The source of the Zeus malware has not been traced by IT staff which has prompted the County to stop using its online banking system for the time being.  

To block future attacks, the accounts department will use a PC isolated from the Internet without email or even USB connections to conduct all online transactions, official said.

The sum was most likely chosen to be small enough to test out the detection of the fraud systems in use by the bank after which the criminals might have returned to help themselves to more.

Banking Trojans such as Zeus (also known as SpyEye) have become the most dramatic and successful forms of malware of recent times. Despite more awareness of their potential, this case shows that they continue to leave a trail of financial destruction – or near destruction - in their wake.

Beyond the weakness of banking systems and the sophistication of Zeus, the malware's success has been aided by its business model which sees it sold to criminal gangs, sometimes through middle men. This has put it into the hands of non-technical professional criminals across the world willing to use it to target specific banks using local knowledge.

In November a UK-based gang was given heavy sentences for one of the largest ever Zeus malware bank frauds yet prosecuted.