What part of speech is secure, as used in this excerpt?
Secure, here, is an adjective.
What word is secure describing?
Software. The software seems secure. Therefore, <u>secure</u> is an adjective attributing a characteristic to the noun: <u>software</u>.
What does secure mean, as used in this excerpt?
It means safe. It means that that piece of encryption looks like something that will not cause you problems.