How do I know if Java is installed on my iMac?

The update will not appear unless you are running Java on your Mac.

In terminal.app copy and paste:

sudo /usr/libexec/java_home

enter your password and return (password will not be echoed.)

Here is a good overview:

http://reviews.cnet.com/8301-13727_7-57408841-263/how-to-check-for-and-disable-j ava-in-os-x/

As stated, this update only shows up in Software Update if you have Java installed. But if you aren't sure whether you may have installed that already or just want to know if you have Java, try opening the Java Preferences app, found in /Applications/Utilities. If it complains and asks you to install a Java runtime, you don't have Java. If it opens up without complaint, you do.

Are you sure it only shows up in Software Update if Java is installed? This update "tool" is intended for Lion users that do not have Java installed, so it would be kind of stupid if it only showed up when it wasn't needed.

When I answered, I don't believe that the "Lion with no Java" update had shown up in Software Update yet. At this point, though, every machine running 10.6 or 10.7 should see a Flashback-related update in Software Update... unless it has already been installed.

Looks like this happened today, within the last 12 hours in fact:

It appears in Software Update as "Flashback malware removal tool" version 1.0.

I have no Java runtime installed, nor is it enabled in any browsers, and java_home results in this:

Johns-iMac:SystemConfiguration john$ sudo /usr/libexec/java_home

Password:

Unable to find any JVMs matching version "(null)".

No Java runtime present, try --request to install.

Johns-iMac:SystemConfiguration john$

I was offered no other Java-related software updates until now.

I can only conclude Apple released this update in an abundance of caution.

John Galt wrote:

I can only conclude Apple released this update in an abundance of caution.

Perhaps it is intended to protect Lion users that might install an unpatched version of Java in the future, like say from a saved, now out-of-date download?

Probably, but I imagine the dirtbags that wrote Flashback are already working on another.

Version 1.0 of this "malware removal tool" is not likely to be the last 😟