it's verye asy to deal with all these actually, about exchange just don't leave a big amount there, only small one for trading, against malware i have a dedicated machien that will never install anythign other than bitcoin
just be carefull to install the version from official source on bitcointalk check the checksum, i'm more worried about soemthign they didn't mention there, and it's being scammed in real life
if they know you have bitcoin someone could murder you to steal your money....
If you're unlucky you can get screwed up anyway. You send money to an exchange with an intent to sell and withdraw, but the transaction gets stuck for a day due to network overload (spam) and you go to bed tired of waiting. On the next day you wake up, go to work, in the evening you check your balance... and boom the exchange was hacked or raided or whatever. People were sending money to gox and trading, all was fine and one day when they wanted to withdraw nothing was coming out. They messaged the support and heard that there are delays...
I'd e more afraid of someone attacking me to steal my fiat than bitcoin. Wallets are useless without a passphrase. Bitcoin still offers a much better security than cash, crooks have to blackmail or torture you to get it.