Yes they can be hacked. Hearing the news about exchanges been hacked, what more these wallet are more likely to be hacked. Less news of wallet hacking simply because hackers are still focus on bigger exchange. So, better to improve the security features of every aspect of cryptocurrency industry.
If we will not secure our private key or password there is a big possibility that it might be hacked. Sad to say it is very hard to retrieve that again, since it has no third party involve in crypto world. Nobody you can run to, no one you can blame on it. Government has no control to your money in crypto so its our responsibility to take care of it, to make it safe from hackers.