Web pages belonging to the US Consulate General in St Petersburg were compromised by hackers earlier this week and used to host malicious code.
Cyber-criminals planted code known as Mal/ObfJS-C which attempts to load further malware from a remote server.
The malware included an additional script that attempted to exploit several browser vulnerabilities in order to install a Trojan on the computer of anyone viewing the site.
Fraser Howard, principal virus researcher at Sophos, said that the attack is part of a larger campaign by cyber-criminals which has infected around 400 web pages on vulnerable servers.
The majority of the compromised pages were hosted in Russia. Sophos said that the infected pages on the US Consulate General website had since been cleaned up.
"This latest attack highlights the fact that no organisation is immune from infection, and that no matter what the size of the company it must defend its web pages fully to avoid being stung," said Howard.
"Unfortunately, while high profile sites such as the US Consulate can be cleaned up quickly, a dangerous number of companies are failing to act responsibly to retain the sanctity of their sites."
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