Getting hacked in Diablo 3 is a very serious issue as real money will be involved soon and this will attract a large number of hackers.
The effects have been already seen in World of Warcraft, a player can lose his gold and items from a character and even get his character deleted as the hacker will gain full control over his account.
If you got your Diablo 3 account hacked, Blizzard will restore your character and items but only once. If you get hacked twice, you will lose your characters and items for good.
Tips for how to avoid getting your Diablo 3 account hacked.
How an account gets hacked? This is simple. The hacker just needs to retrieve your battle.net password.
If you visit certain websites that are containing keylogging software, that software will auto-install itself on your PC and the next time you try to login into Diablo 3, the software will send your password to the hacker.
The software might also block Diablo 3, making it unable to run or pass loading screens.
To avoid getting such malware software, avoid visiting any website that might seem suspicious, a strange URL, avoid clicking on links too fast without checking the URL. If you must check a website, write it first into Google web search and see if it looks ok.
These links are posted on Diablo or gaming related websites. Mostly on the official Diablo 3 forums.
Other than these, there isn’t much to worry about, you can play Diablo 3 safely without even an authenticator.
Getting your account hacked by joining public games is just a rumor confirmed also in a blue post from the Diablo 3 official forums.
Last thing, if you got hacked, visit battle.net, the help section for Diablo 3.