The US Treasury's Bureau of Engraving and Printing has been attacked by hackers.

The Bureau, along with three other official government web sites, were targeted in an attack that redirected visitors to web sites containing malicious content.

The websites affected were BEP.gov, BEP.treas.gov, Moneyfactory.gov and Moneyfactory.com. The sites were taken down as soon as the breach was discovered.

According to security experts at anti-virus software maker AVG, the web sites were hacked using an iFrame application that injected malicious codes into the site. The malware was used to send data to computers somewhere in Ukraine. 

Roger Thompson, chief research officer at AVG, told tech blog V3.co.uk: “City and country-level sites get hacked all the time in the US and UK but it’s very unusual to see an attack like this.”

Thompson added that an initial study of the attack shows that there was an 80 per cent chance it was mounted from a third-party site visitor counter. If this was the case, he said, the problem might be difficult to fix.