bitcoin itself as the protocol/platform has proven to be quite solid
the trick is to not keep coins in exchanges unless you are into trading, but then you know that you are taking a risk
It has a lot more to do with bad code, bad storage policies or bad intentions on the part of the exchanges, and most of them point to transaction malleability - a design flaw in the original protocol - as their excuse.
There are several exchanges in the works but they are bogged down with regulation and not able to open.
I don't know whether that's true, but that's what s/he wrote. It's an easy enough to understand and plausible notion.
Bitstamp seem to be doing the right things but I doubt that they can legally operate in US or take transfers from/to US as they are doing.
There have been a couple of these actually:
http://www.pcworld.com/article/2109000/bitcoinstealing-malwa...
http://www.computerworld.com/s/article/9244772/Bitcoin_marke...
http://www.coindesk.com/cointhief-mac-malware-steals-bitcoin...
And the most famous probably, cryptolocker - http://en.wikipedia.org/wiki/CryptoLocker ...though this is more a ransom strategy than just out-right theft.