Bitcoin users have been urged to switch to pool mines that fully validate data blocks, after the virtual currency system hit a major snag during a planned upgrade.
The open source P2P community warned on Saturday that "many wallets" were "currently vulnerable to double-spending of confirmed transactions."
Anyone who received bitcoins in transactions that were validated before 15:00 UTC yesterday were unaffected by the upgrade blunder.
However, for users of certain client software – such as Lightweight (SPV) wallet and Bitcoin Core 0.9.4 or earlier versions of that app – "confirmation scores are significantly less reliable".
The "invalid blocks" generated by some miners appeared to remain an ongoing problem for Bitcoin users. The community was yet to provide a fresh network alert at time of writing on Sunday.
In its 4 July update about the upgrade glitch, the community said:
The problem is miners creating invalid blocks. Some software can detect that those blocks are invalid and reject them; other software can't detect that blocks are invalid, so they show confirmations that aren't real.
Apparently, a number of large miners had spaffed $50,000 as of Saturday.
It seems that the best advice – for now, at least – is for users to run the latest clients of apps such as Bitcoin Core, which will spurn dodgy coins.
Meantime, the community has been attempting to fix the flaw. ®