On Monday, the Bitcoin world had a meltdown as the cryptocurrency’s network started to slow down seemingly without explanation, leaving people’s transactions in digital limbo.
Now, it looks like at least part of the reason for the slowdown might be a concentrated attack on Bitcoin by unknown actors.
The issue is that the digital “blocks” that contain every Bitcoin transaction are being filled up. Transactions are put into blocks by Bitcoin users, who are incentivized in part by fees that people attach to their transactions. Transactions aren’t complete until they’re put into blocks, or “confirmed.” But with near-full blocks, there’s more competition for space inside them, and so miners logically seek out the transactions with a decent reward attached before those that don’t—meaning those who are willing to pay more in fees will get their transactions confirmed first.
http://motherboard.vice.com/read/is-bitcoin-under-attack-spam-fees-block-size-debate
