Real hacking is taking advantage of security vulnerabilities in either the Cipsoft servers and the software supplied by Cipsoft. It's almost unheard of for people to lose their accounts due to this and nearly all of the time "hackings" are just the result of carelessness or straight out cheating and is completely avoidable. If you follow the Tibia rules and use a little common sense (or not so common it would seem) there is absolutely no reason to ever get hacked.
Downloading Cheat Tools
This is probably the largest source of "hackings". Most cheat programs have keyloggers in them, no virus scanner software will detect them and they can even slip under your firewall undetected. Even things like skill calculators, if you've downloaded my TibCalc and you're not one of my friends how did you know it was safe? Well, you didn't and you risked losing all of your stuff. Just because I don't put keyloggers in my stuff doesn't mean others are honest too, when ever you download and run such a program you risk giving someone else full access to your account and losing everything you have, is it really worth it?
Playing Tibia From LAN Houses/Internet Cafes
If you play from a LAN house where a lot of people play Tibia you're going to get hacked. Other players will probably install keyloggers on the computers, and those keyloggers don't even need to connect to the internet so they're nearly impossible to detect. Other players will probably also install cheats that will install keyloggers. Playing from a LAN house is one of the most stupid things you could ever do if you value your character.
Character sharing is against the rules but many many people still do it. A lot of the time when people claim to of been hacked a "friend" who they share their character with has simply just stolen all of the items and made out like the character was hacked.
Visiting Links Posted In Trade And Game Chat
If someone is posting a link to a web site in trade or game chat it's most likely something to try and rip you off, wether it be a site that has keyloggers in files, makes use of IE exploits to install software on your system, has a fake login panel or whatever. If someone's posting links in game just put them on perm ignore and forget about it.
Using An Insecure Email Address
Your Email address is like your "spare set of keys" to your account. If someone gets into your Email account they have full access to your account. First of all don't use a Yahoo or Hotmail Email address, they are just too easy to break into. Secondly never tell anyone your Email address, if no one knows which Email account you're using they can't even begin to try to break into it.