Do you know any Device can easily be hacked through Wi Fi connection ?

Let's start at the router the easiest way is a WPS attack, - too stop this just disable WPS within your router settings. Another way is brute force most routers from ISP will use same combination of characters for example Virgin UK routers are 8 lowercase letters excluding i and o. While there is no way to prevent a brute force attack you can make it alot harder. Which brings me on to dictionary attacks, now the name isn't exactly as implies there are "dictionaries" out there they have been made up of compromised accounts like to rock you dictionary, an attacker could run this against your wifi password and may get lucky. - Best way to prevent these attacks are to have a passphrase of atleast 5 words. Diceware is a pretty good method of creating passphrases.
Now let's say I managed to get on your wifi network, there are many things I could do I could perform man in the middle attacks to get your social media passwords etc. Also could access your computer. Many people have sharing enabled so I could see all your files that have been shared, another flaw people have is not actually passwording their computer, mainly due to ease of use.

Firstly turn sharing off and secondly set a password/passphrase to login to your computer while its annoying to type passphrase everytime you need to use PC its the price you pay for security.

Lastly if you have passworded your account and have sharing turned off there are still ways, Windows XP for instance is riddled with vulnerabilities, as is alot of the Windows OS's always keep upto date with windows updates they are extremely annoying but there for a reason.

Hope this post has helped.