What is a block eruptor ? I see all these little usb devices for $60 or thereabouts. Are these things legitimate mining platforms? Or is there some other function? I just see mention of them... haven't seen a good page explaining it.
I heard they can be used to mining other coin too
Block Eruptors are USB connected and powered devices that are designed to do just one thing: create hashes based on the SHA256 algorithm.
They can do anything that uses the specific subset of SHA256 (SHA256d specifically) that this thing can calculate.
We, as miners, use them to mine coins. Any coin based on SHA256d will work, but you could use them for other SHA256d cryptographic purposes, like password hashing, brute-force password cracking, creating an encrypted data tunnel (VPN), SSL-like certificates, encrypting Word documents or Excel spreadsheets, etc.
You just need to develop a piece of software that will send any encryption commands to the Block Eruptor. For a VPN, you'd need to create a piece of VPN software that will push all transfers through the Block Erupter before sending it off through internet.
So yeah, they can be used for any purpose that requires SHA256d hashing. However, software to support that is yet to be developed.
As soon as Block Eruptors become obsolete, it'll be more likely that someone actually will develop software like that.
Edit: it really does nothing more than hashing in SHA256d.
Think of it like Ceasar Cypher. You take the alphabet and assign a number to every letter. When you send a message, you change all letters to numbers and the reciever has a conversion table.
Anyone in between cannot read the message without the conversion table. If the mailman opens your envelope, he cannot read what's inside unless he is in posession of the conversiontable or spends hours (or even days/weeks) trying to decypher the message.
So the Block Eruptor is essentially nothing more than a sort of automated conversion table device. It will encrypt and decrypt a message.