If the data is worth backing up, isn't it worth keeping it safe?
If you read the Terms & Conditions of the free sites, all that I have seen say they have the right to do just about anything they want to do with your data including making it available to others for online viewing or downloading.
Find a site that is cheap but not free and in the USA.
Although I am not a fan of McAfee security products, they have about the best deal at $59/year and unlimited storage.