How to hide strings in a exe or a dll?

Question

I discovered that it is possible to extract the hard-coded strings from a binary.
For example the properties view of Process Explorer displays all the string with more t

Answer 1

Will all your secret codes be GUIDs or was that just an example?

Perhaps store your secret as a binary guid:

const GUID SecretGuid =
    { 0x4537774B, 0xCC80, 0x4eda, { 0x7A, 0x9E, 0xE7, 0x79, 0x91, 0xF5 } };

Then convert your supplied guid from string to binary format and compare the two binary guids.