Apple are active with iOS updates recently with another one just hitting iTunes for iPhone, iPad and iPod's.
As you can see from the details in the update below, this is just a small update which patches a security vulnerability with certificate validation.
iOS 4.3.5 Software Update
Fixes a security vulnerability with certificate validation.
Products compatible with this software update:
iPhone 4 (GSM model)
iPod touch (4th generation)
iPod touch (3rd generation)
Plug in your iDevice and get updating now!