Recently apple released iOS 4.3.4 to remove the jailbreakMe exploit. Just week after that apple has now release iOS 4.3.5 which is suppose to fix security vulnerabilities with certificate validation.
All Apple hardware that can run iOS 4 is supported. Verizon iPhone has a similar fix available, labeled iOS 4.2.10.
Users which are using non-jailbreak iPhone, iPad, iPod touch are recommended to download this update as soon as possible. You can grab the update by plugging your iOS device into iTunes and hitting the “Check for Update” button. It will automatically start downloading and installing updates.
However, If you have a jailbroken device, you are advised to stay as far away from this update as possible.
Direct Download Links for iOS 4.3.5 (Official from Apple)