I could create a program to randomly shuffle words in 24 word strings (the most words MultiBit allows to create a private keys with), to create private keys and check them for a BTC balance on the block chain. If the keys' address had BTC allocated to it, I could simply withdraw it to my own, untraceable wallet.
I suggest you try it. Electrum version 1 wallets uses 12 words, half of Multibit. Create the script and run it for a month. Electrum uses a list of 1626 words, total permutations is 3.4 x 10^38. Have fun with it! You might just be lucky and hit a wallet with balance on the first attempt.
I think there are people who tried it before and some still hacking. I haven't heard of any Electrum users reporting that there coins are mysteriously gone.
as I mentioned in another thread, you could have 10,000 supercomputers each running 100 petaflops for a whole century and not even get through one percent of one percent of the combinations...oh and that's before electrum's key stretching which makes it 100,000 slower to compute. it also doesn't include any extra time needed to generate multiple addresses for each seed and check their balances...so....good luck.