Just some random question.. How can a dev. change a coin while its already out? If dev. can do it cant a hackers also do it? sorry hope you understand my noob question.
Sure they can.....after convincing everyone in the community (or rather, the Devs, exchange people, pool operators and merchants and other stake holders, who make all the announcement that all the other
sheep coin users/miners follow) that they need to upgrade to the new client that has the protocol changes. This is what's known as a "hard fork".
But, if everyone in the community doesn't upgrade to the new client in a timely manner (or the community splits), you'd end up with two separate but (presumably similar) coins. Those that upgraded cannot send to those who have not upgraded, and those that have not upgraded cannot send to those who have. Miners who don't upgrade will end up mining blocks that will never be recognized on the new network, and vise versa.
In fact, if everyone ran both versions of the client simultaneously, but with the same wallet.dat file, and you received coins to the wallet in both versions from people who used one client or the other, then you will end up seeing two separate balances. Similarly, if you decided to go on vacation and left your mining rig going (possibly in a solo mining situation with several hundred mega hashes), and then 3 days later the community found a huge security risk in the coin wallet that needed to be fixed with hard fork, then for the next 27 days you will end up mining blocks on a network that was been largely abandoned by the rest of the community (resulting, effectively, in a loss since no exchanges or merchants one will accept coins from the old network).
Hence, if you have any coin holdings or you are mining, it behooves you to maintain awareness of any news surrounding the coin that may arise. While extremely rare, and quite drastic, it does occasionally happen and you need to know what to do when the scenario occurs (generally achieved by reading what others are saying and go with the general consensus).
Yes this applies to mining. But id certainly imagine, say for example you have your wallet with x amount of coins and you forget about it for a year and the wallet changes, even multiple times. The wallet.dat file should always remain compatible so when you do return to claim your coins you should simply be able to update the wallet, copy your wallet.dat file and retain your coins right?
As long as you didn't do anything, your coins will remain the same. But if a scammer using the same outdated client as you were to pay you in the outdated currency and you shipped product without knowing about the mandatory update, then you're pretty screwed.
Basically, you can take the exact same wallet.dat file and end up with two separate balances: 1 that exchanges and most other people are using, and 1 the few people will ever use or mine on ever again.
So if the update took effect at block 100k lets say, then the coins up to that point will be the same. But if for sh*ts and giggles you were to still have a copy of the old client after several years, you would find that you still have those old coins and can trade them to anyone else who still mined on it (or even mine it yourself solo, probably for next to no difficulty).
Even more interesting is that if the new wallet had some fatal error in coding that completely messed up the coin, the community can always revert back to the old client with minimal issues.
Something to think about.