It seems to me that everyone is thinking about the threat from hackers, especially, say large, well-organized groups of hackers.
But what about another threat: casual guessers.
Suppose someone develops a screen-saver that guesses intelligently, and everybody just keeps running it trying to win the bitcoin lotto.
Could the bitcoin network handle it when only one in ten trillion transactions are legitimate?
Sincerely,
Joe.
Transactions that are invalid will not be propagated by the network, they will stop at the first node that will get them. If someone spams the network with invalid transactions, they can be ignored by the nodes.
Guessing someone's key is so improbable, that not now it is impossible to get any results.
Spammers and scammers probably won't target Bitcoins for awhile - people using them are too few and far in-between. People writing viruses are more harmful nowadays, whether they steal wallets, or botnet your computers into mining.
