Once upon a time Apple released their own Java updates but they were slow to react to exploits and this lead to 600,000 Macs being infected with the FlashBack Malware earlier this year.
Recently Oracle took back the responsibility for keeping Java up to date and almost immediately there is an issue.
They have released an urgent update that should be downloaded and installed as soon as you can. You can find the software on the Oracle website.
If you have regular health checks this will be done for you but if not, or if your next check is sometime away, please download and install as soon as possible.