What is hex editing? Hex editing is a method of altering files based on hex instead of using given editing software, such as notepad or visual basic. This is not the quickest method of altering a file, but it will allow you to access portions of files that are otherwise concealed.
So is this a security concern? Absolutely. hex editing can be used on data in system memory as well as data stored on the hard drive.
Here I'm using FlexHEX. You can see that selecting the hex will also show you the plain text translation, and vice versa.
This is how easy it is to edit the text in a text file. You can also alter checksums as such:
Note that I did not alter a file from an actual program, because it is illegal. Tampering with any files from an installed or running program is considered reverse engineering.