Android Question App security, Encryption?

Hello,
First of all you should use the obfuscation provided by B4A (Release obfuscated). It is a first step.

1) Is the excel sheet itself protected?
2) Are you storing the correct username/password combo in plaintext?
3) Is your algorithm sensitive or just the information it handles?
4) Are you storing the post-processed information in a file?

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1) The information source itself MUST be protected, there are a few ways to do it. If needed we can point you in the right direction.

2) Storing login information in plaintext is a huge mistake, you MUST hash the user/pass combo, preferably "salted". Again, there are many tutorials on this subject around the web.

3) If your algorithms are sensitive enough themselves to be secured, these parts of your code should be separately compiled as native (.so) library.

4) Your post-processed sensitive data should only be stored if absolutely required. A good practice would be clearing all the variables and data structures once they done their job. The memory should be cleared as well in Activity_Pause, so that it would, at least in theory, impossibilitate any memory scanners from sniff your data.

Thank you for the answers. I will do a obfuscated release. The excel sheet itself is loaded onto a panel and I hide the panel. So what more do you think I can do?

The algorithm isn't sensitive, it's only the table that is loaded onto the panel that contains the sensitive information.