It's not every day that the U.S. Department of Homeland Security makes an urgent recommendation to computer users. But they are doing so now, asking people to disable Java software because of a newly discovered security Relevant Products/Services vulnerability that opens up millions of computers to criminal hacking.

The warning comes after a security flaw was discovered earlier this week that experts say could be used to attack Relevant Products/Services computers. Several popular exploit kits, which are tools used by criminals to attack vulnerable computers, have recently added the ability to exploit the newly found flaw.

Java is installed on millions of Mac, Windows and Linux computers worldwide via browser plug-ins, and users are being advised to disable the plug-ins.

'Like Open Hunting Season'

One security expert told the Reuters news service that the current situation is "like open hunting season on consumers," while another described Java as "a mess" that is not secure Relevant Products/Services.

Generally, consumers do not need Java in their browsers, but some businesses may be using it for online activities. For instance, Java is utilized in Citrix's widely used online collaboration software, GoToMeeting.

In a posting Thursday on the Web site of its Computer Emergency Readiness Team (CERT), Homeland Security said that the "Java 7 Update 10 and earlier contain an unspecified vulnerability that can allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable system."

It noted that a remote attacker could convince a Web user to visit a specially made Web page, which could then carry out the attack. The attacking code could infect a well-known, legitimate site as well as ones with lesser credibility, and then stage the attack from there. Since there are no known practical solutions, the agency recommends that users disable Java in Web browsers.

Instructions for Removal

Oracle, which acquired Java when it bought Sun, has a page that describes how to disable Java for all browsers on Windows machines, or individually by browser on any platform. The instructions, How Do I disable Java in my web browser?, are located at http://www.java.com/en/download/help/disable_browser.xml

One of Java's strengths increases its vulnerability -- its much touted ability to run the same code on multiple platforms. This "write once, run many" ability can be very useful for developers, who then can avoid having to create different native versions for a variety of different operating system configurations. But if there's a security flaw, Java's strength can also become a criminal hacker's dream scenario.

In August, a comparable security scare led security experts to warn of such a vulnerability, and to recommend using Java only when needed. In September, the government of Germany advised its populace against using Microsoft Relevant Products/Services's Internet Explorer until that company patched a vulnerability. In October, Apple removed old versions of Java from all Mac-compatible browsers when Mac users installed a new OS X version, and both Apple and Oracle declined comment about the action.