Well, trust no one, be your own bank...
In some cases (when you have 2FA enabled and all security options set) it will be harder for anyone to break into your blockchain.info online wallet.
If the wallet was encrypted they have easily access too?
2FA is good but in this case, if the hackers stolen the private keys, it will have no value. Well, lets keep the pc clean to avoid hackers
If it's an online wallet like BLockchain.info (where the service has no information's in their servers) then yes , since the wallet will get decrypted in your browser as far as I know and that should give the hacker a way to hack you.
As for desktop wallets ,If your machine is infected (there will be most likely a Keylogger on it) , as soon as youe type the password to decrypt the wallet , RIP funds.