Apple acknowledged Tuesday that a flaw in Oracle’s Java software has left Macs open to the Flashback botnet.

In a page on the company’s Knowledge Base Web site, Apple said that it is working on a tool to recognize and remove the malware. The company has already released an updated version of Java that plugs the hole, but had yet to release an easy way for the average computer user to find out if they had been already affected by the botnet.

Apple is also working on the larger problem, it said.

“In addition to the Java vulnerability, the Flashback malware relies on computer servers hosted by the malware authors to perform many of its critical functions,” the company said. “Apple is working with ISPs worldwide to disable this command and control network.”

The Flashback trojan is estimated to have affected around 600,000 computers, and can serve as a reminder to Mac users that their machines aren’t impenetrable. While Macs have enjoyed the reputation of being far less open to viruses than PCs, as Apple’s market share has grown, some hackers have started to take notice.