It's strange that they would've been able to steal both your BTC and LTC just like that. The email trap would have to be pretty sophisticated to achieve something like this. Did you confirm that it was indeed the email link that caused you to lose your coins? Did you consider other possibilities? Do other people have access to your computer?
If the OP's wallet files had no or weak passwords then it would have been trivial to get the private keys. Another possibility is that the OP had entered his wallet password after his computer was infected with the malware on his both LTC and BTC wallets which would have caused the unencrypted wallet files to be temporarily stored in RAM while the wallet software is signing the transactions.
This is an example of why it is important to use a strong wallet password (that you do not store on your computer). If you do this and realize that your computer has been infected with malware then you can quickly recover your wallet from a backup on an alternate computer and spend your funds to another newly created wallet/address that was created on a computer not infected.
If you enter your wallet password on your wallet software after your computer is infected with malware then there is not very much you can do to prevent your money from being stolen. The only thing you can really do is change the settings on your wallet software so that it will store your unencrypted wallet keys in RAM for as little time as possible, this will force you to enter your password every time you spend funds in your wallet however it will give the malware a shorter amount of time to grab your private keys, most of the time this will not result in keeping your money safe, however it will with a very small subset of malware. Another thing this will do is protect you from physical theft of your computer because if your computer if physically taken from you shortly after you spend your Bitcoin then the attacker will likely not have access to your unencrypted private keys.