Ok so you've taken all of the precautions we have outlined, but something has gone wrong and you've woken up to discover one of your poker/casino site accounts is drained. In this situation, the faster you act the more likely you are to see some of your money again. Note none of the poker sites accept responsibility for money theft. They will do their best to help out, but if the money has already disappeared they won't reimburse you.
A typical scenario is that somebody obtains your account details and then logs on as you. The withdrawal systems on the poker sites are configured to ensure they won't just be able to pull all of your money out of the poker account and dump it to their own bank account since your poker site username is tied to your bank details.
So how do they move your money? The hacker will probably play at an online poker table, using your account and proceed to lose your cash in your account to their own dummy account, before withdrawing the funds once they are in their account. Another option they may employ is to move your funds via a simple player to player transfer, which most poker sites facilitate.
It is usually obvious where your money has gone to, and it is often just a matter of whether or not the withdrawal has been processed by the time you work it out.
Depending on which poker site you use and what withdrawal service you are using (bank wire, cheque, withdrawal to E-Wallet, etc), a withdrawal could be processed in any time from a few minutes to several days. If it has yet to go through, the poker site can freeze their account and stop the cash in its tracks. If not, you are out of luck, as there is no real legal recourse if this happens to you – primarily because these companies operate in other countries.
Your best bet if this does occur is to immediately call up the customer service line for the poker site in question, as well as mailing their support address and basically doing everything you can to alert them as fast as possible. From there it may take days or weeks before you get a proper resolution, but if the money hasn't left the site's system then you have a good chance of recovering it.
Another good tip to help mitigate the damage is simply to cash out regularly. Never keep more money online than you require to play at any one time and try to diversify, keeping it in a couple of different places.