What was going to happen (BIP148)
A number of months ago, the community decided to coordinate the activation of Segwit on August 1st, rather than continue delegation of this coordination to the miners, who had collectively been stalling the upgrade. This proposal was numbered BIP148, and widely supported by Bitcoin users. There was fear that 51% of miners might retaliate by splitting the blockchain, using invalid blocks light clients could not detect in order to solidify the split in perpetuity.
Why BIP148 is no longer relevant
Last week, miners finally decided to stop stalling Segwit, and have begun the activation process on their own, prior to BIP148’s August 1st flag day, and in a manner that is essentially embracing BIP148 themselves using a miner-activated method early. Therefore, BIP148’s new rule is redundant, since miners are already enforcing it as of Sunday. Users should still run BIP148 code to ensure they retain full node security, but the probability miners will attempt to split the chain in retaliation at this point is pretty much zero. Basically, BIP148 was an early success.
New altcoin launching August 1st, “Bitcoin Cash”
In the meantime, a new altcoin calling itself “Bitcoin Cash” has been formed, aiming to take advantage of the previous talk of an August 1st fork, to try to hijack Bitcoin users for their altcoin. By using the name “Bitcoin”, they may fraudulently fool people into switching to their new altcoin.
But at the end of the day, “Bitcoin Cash” (or, perhaps more accurately called, “Bitmain-coin”) is just yet another altcoin. It has no effect on the real Bitcoin network, and users who stick to Bitcoin Core and compatible full node software will be entirely unaffected.
Note also that this isn’t a particularly unique or even first-of-kind altcoin: “Bitcoin Dark” and “Bitcoin Plus” have tried to hijack the “Bitcoin” name previously. Bitmain-coin also gives a premine to all Bitcoin holders as of their launch date, but this too has been done before, by an altcoin called CLAMs and another more recent altcoin calling itself “Bitcore”.
However, there is a “gotcha”: At least the current Bitmain-coin code will use the original Bitcoin directories by default. This means if you wish to install or use Bitmain-coin yourself, it will mess up your Bitcoin installation! Using both together is outside the scope of this blog post, however, and I personally will only be supporting real Bitcoin.