To say that iCloud is a big deal for Apple is a bit of an understatement. The cloud-based storage and backup service was launched just 6 months ago, alongside the iPhone 4S and iOS 5, and has already garnered more than 100 million users.

But its quick rise in popularity and deep integration into Apple’s software has led to one major question: how secure is it? Well the folks over at ArsTechnica recently spoke with some software security experts to find out…

According to Robby Gulri, Echoworx’s vice president, iCloud uses the best security practices in the industry including SSL transmission and on-disk 128 bit encryption. He also commends Apple for its recent move to ban developer access to Unique Device IDs.

That’s the good news. The bad news, however, is that if Apple ever wanted to, it could view any and all of your iCloud data. Forensic data analysis expert Jonathan Zdziarski points out an interesting portion of iCloud’s Terms and Conditions:

“However, Apple reserves the right at all times to determine whether Content provided by others and has no duty to pre-screen such Content. However, Apple reserves the right at all times to determine whether Content is appropriate and in compliance with this Agreement, and may pre-screen, move, refuse, modify and/or remove Content at any time, without prior notice and in its sole discretion, if such Content is found to be in violation of this Agreement or is otherwise objectionable.”

So how does Apple access your information if its encrypted? Ars explains that the company “holds the master decryption key” which would enable it to essentially decrypt and review any user’s iCloud data if needed.

Should you be worried? No. The bottom line here is that your iCloud data is well-protected — well, from everyone outside of Apple. And it sounds like they will only access your files if it’s pertinent to a legal matter.

Do you use iCloud? Do you ever worry about security?