Trend Micro has spotted a piece of malicious software that masquerades as the latest patch for Java, a typically opportunistic move by hackers.
Oracle released two emergency patches on Sunday for its Java programming language and application platform, which is installed on millions of computers worldwide.
The latest version of Java is Update 11. Trend Micro wrote on its blog that it was alerted to a fake "Java Update 11" present on at least one website. If a user installs the bogus update, a malicious backdoor program is downloaded.
"Once executed, this backdoor connects to a remote server that enables a possible attacker to take control of the infected system," wrote Paul Pajares, a fraud analyst with Trend.
Hackers often disguise their malware as a legitimate software update in the hope of confusing IT staff. Interestingly in this case, the fake update doesn't actually exploit the vulnerabilities that Oracle patched on Sunday, Pajares wrote. The user is tricked into downloading a different piece of malware.
"The use of fake software updates is an old social engineering tactic," Pajares wrote. "This is not the first time that cybercriminals took advantage of software updates."
Pajares advised users to download updates only from Oracle's website. Trend Micro, along with other computer security firms and experts, are generally advising that users uninstall Java if it isn't needed, which helps eliminate exposure to the risks from software flaws.
Users can also opt to keep Java on their computer but disable it within the Web browser, which is how the latest vulnerabilities exposed users to attack.
The two vulnerabilities patched by Oracle on Sunday both could be exploited by a malicious "applet," a Java application that's downloaded from another server and runs if a user has Java installed. Applets are often embedded in Web pages and run in the browser.
Security reporter Brian Krebs wrote on Wednesday that a zero-day Java exploit for an apparently brand-new vulnerability was being advertised for US$5,000 (£3,129) in an underground hacking forum. The advertisement was posted for a short time, then disappeared, Krebs wrote.
Oracle officials did not respond to an email request for comment.