I wonder what will happen if my computer got stolen.
Can a hacker gain access to the files on my computer?
I have Ubuntu 14.04 and have not installed any security programs - should I do something to protect myself against this?
I know you're likely not worried about state secrets or very valuable data, but the correct answer is "Yes". Someone with physical can always access your files, always. Full disk encryption makes the process significantly slower (time could be measured in years or centuries), but the attacker can access your files.
See the 10 immutable laws of security. Law 3 specifically states:
If a bad guy has unrestricted physical access to your
computer, it's not your computer anymore
The article goes into a number of great ways you can get owned here, including but not limited to making a copy of your disk, adding a keylogger and giving it back to you. Once you enter the password, the malware can send it back to the attacker, letting him decrypt his copy of your disk.
And never forget what xkcd has taught us:
Passwords are insufficient if you are not torture-resistant
If you're not worried about the NSA, or other groups willing to spend millions of dollars, years of time, or torture you, full disk encryption is probably fine. But it does not mean that you are 100% safe. Storing no data on your laptop and only VPN'ing to a secure machine is probably a better idea. Don't forget MFA and your tin foil hat.
