We already know that there was new security vulnerability has been found on Java 7 and Oracle released Java SE7 U11. But it didn't fixed the security issues and still there was some security holes. After Apple blocks Java for second time, Now Oracle released Java 7 update 13.
This new update fixes over 50 security issues. Most of them are specific to java usage in web browsers.
If you have installed Java on your PC/Laptop, first Uninstall the old version. Download the new version
Java 7 update 13 from java.com and install it.