5) Encrypting the Dash Wallet
After fully synchronizing with the Dash network it's highly advisable to encrypt your Dash wallet with a password. Using a password you have never used before and is impossible to guess is the safest way to go with. Please review the Strong Password Ubuntu Documentation to ensure you safety even further.
https://help.ubuntu.com/community/StrongPasswords
Note: Make sure to keep your password safe somewehre so you will never lose it or get it stolen.
To encrypt your wallet click "Settings" and click "Encrypt Wallet...".
Now it should ask for a passphrase, enter your password in both fields and click "OK". It will ask for a confirmation, click "Yes".
At this point the wallet will be encrypting itself so don't click anything. When it's finished you will see this notification screen. Please read and understand it and than click OK.
The Dash Wallet will close, you can start it again by clicking the Dash-qt file.
Your wallet is now encrypted (hopefully with a strong password). Remember to save your password in a safe place, without it you will be able to access your funds.