TL;DR: If your balance shows 0 and there are confirmed transactions in your history. Then you have been robbed!
Seems like some fraudster tripped many people with an unsuspecting website http://iotaseed.io
As everyone know, to create IOTA wallet, we need to create a 81 character seed. For those who have good knowledge of computers and privacy created their seeds locally in a secured way. However, lot of beginners who wanted to create seed went to google and searched for “Generate IOTA Seed” and the top result was an unsuspecting website http://iotaseed.io
When you go that website, you need to move your mouse pointer randomly and it generates a seed for you, which you back up and also use to login to your wallet. One important thing, everyone missed is those buggers started storing keys generated for all the while.
Now starting on January 18th, they have launched a planned attack with all the seeds stored and have stolen funds from most of these beginners.
Source: To everyone posting with stolen balances
Nic Carter giving a walk through of events happened