Computer users are still being told to disable the Java software in their web browsers despite Oracle releasing an emergency patch to fix vulnerabilities exploited by criminal hackers.
"This and previous Java vulnerabilities have been widely targeted by attackers, and new Java vulnerabilities are likely to be discovered," the US Department of Homeland Security said Monday in an updated alert published on the website of its Computer Emergency Readiness Team (CERT).
"To defend against this and future Java vulnerabilities, consider disabling Java in web browsers until adequate updates are available."
Java allows programs to run within websites and powers some advertising networks. Users who disable Java may not be able to see portions of websites that display real-time data such as stock tickers, graphical menus, weather updates and ads.
Vulnerability in the latest version, Java 7, was "being actively exploited," the department said.
Java 7 was released in 2011. Oracle said installing its "Update 11" will fix the problem.
Security experts said that special code to take advantage of the weakness is being sold on the black market through so-called "web exploit packs" to Internet abusers who can use it to steal credit card data, personal information or cause other harm.
The packs, sold for upwards of $US1500 apiece, make complex hacker codes available to relative amateurs. This particular flaw even enables hackers to compromise legitimate websites by taking over ad networks. The result: users are redirected to malicious sites where damaging software can be loaded onto their computers.
Oracle said it released two patches - to address the flaw highlighted by the government, as well as another flaw that the government said was "different but equally severe."
As well, the patches set Java's default security level to "high" so that users will automatically be shown a prompt and given a chance to decline malicious software before it loads onto their computers.