which is best free online web to store data with security ?
What kind of data are you storing?
Yes, your question is much to vague and open-ended for anyone to be able to give you a helpful answer. Please provide more details.
Also as important as what kinds of data (text, documents, etc) is how you want to access that data....
Without knowing what the data is? Nobody will provide you storage of data. If you can go for Cloud then they can provide security. It will be the easy option for you, but it would be paid. You can't store data freely.
Any of them, just encrypt the files before it goes up to the cloud. It is just a bag of scrambed bytes to them at that point no matter how secure or insecure their system is.
i used sitesled.com abt 4 years ago to host data free and they were very good. I don't know what they offer nowadays.
Thank you all for your suggestions, but as the OP seems to have lost interest, thread closed..