Attackers are exploiting a new and unpatched vulnerability that affects the latest version of Java -- Java 7 Update 6 -- in order to infect computers with malware, according to researchers from security vendor FireEye.

So far, the vulnerability has been exploited in limited targeted attacks, FireEye's senior staff scientist Atif Mushtaq said Sunday in a blog post. "Most of the recent Java run-time environments i.e., JRE 1.7x are vulnerable."

The exploit is hosted on a website that resolves to an Internet Protocol address in China and its payload is a piece of malware that connects to a command and control server located in Singapore.

The malware installed in the attacks seen so far appears to be a variant of Poison Ivy, Jaime Blasco, a researcher with security firm AlienVault, said Monday in a blog post.

Poison Ivy is a so-called remote administration Trojan program that has been used in many cyberespionage campaigns in the past.

It's just a matter of time until a proof-of-concept (PoC) exploit is released and more bad guys start targeting the new Java vulnerability, Mushtaq said.

"We have confirmed the 0-day [unpatched] vulnerability to affect Java 7 update 6 build 1.7.0_06-b24 for Windows," Carsten Eiram, chief security specialist at vulnerability management firm Secunia, said Monday via email. "It should affect other versions and platforms as well."

Secunia rated the vulnerability as extremely critical because it allows the execution of arbitrary code on vulnerable systems without user interaction.

"This vulnerability is not a 'memory corruption' type vulnerability, but instead seems to be a security bypass issue that allows running untrusted code outside the sandbox without user interaction," Eiram said. "In this specific case a file is downloaded and executed on the user's system when just visiting a web page hosting a malicious applet."

Joshua Drake, a security research scientist at security consultancy firm Accuvant, published a proof-of-concept exploit for the vulnerability on Monday. His PoC code was then used to create another exploit for use with the popular Metasploit penetration testing framework.

A proof-of-concept exploit for the vulnerability was published online on Monday and was then used to create another exploit for use with the popular Metasploit penetration testing framework.

A Metasploit user also reported testing the exploit successfully on Mac OS X 10.7.4 with Safari version 6.0 and Java 7 update 6.

At the Black Hat security conference in July, security researchers warned that Java vulnerabilities are increasingly targeted by attackers and that exploits for new Java vulnerabilities are being integrated into attack toolkits faster than ever before.

"The widespread use of Java makes it an interesting target in itself," Eiram said. "However, another major reason for why Java is interesting from an exploitation point-of-view is how it's affected by certain bypass type vulnerabilities (like this one); these make it easy to reliably create exploits across different versions and platforms without having to worry about various security mechanisms e.g. ASLR and DEP on Windows."

It's not clear when Oracle will release a patch for this vulnerability. The company did not immediately respond to a request for comment.

In the meantime users are left with very few options to protect themselves. "We are not aware of any fixes or workarounds except disabling/uninstalling Java," Eiram said.

However, uninstalling or disabling Java is probably not an acceptable solution for a large number of companies and users that rely on Java-based Web applications to conduct their daily business.