#After encrypting my wallet, there was a warning that my wallet is still not save in case of a virus. What is the risk? The virus doesn't know my password, does it?

If you have encrypted it, unless the virus runs a brute force attack to crack the passphrase or it uses a keylogger, the wallet should be fine. Just make sure to encrypt it and back it up on another drive\cloud\pc\usb\paper-wallet

http://bitcoin.org/en/secure-your-wallet