First of all, SMB is a network protocol for sharing files. It's sometimes known by the name samba, which is an implementation of the protocol. If you have a remote drive mounted for sharing documents with your coworkers there's a good chance you're using SMB.
This exploit worked in two stages. First, there was a massive email campaign. Then, when employees would click on the attachment, the malware would worm its way onto other computers on the local network using an exploit in the SMB file sharing stack (which orignally came from leaked NSA malware). Then it would encrypt the user's files and demand the ransom.
This exploit worked in two stages. First, there was a massive email campaign. Then, when employees would click on the attachment, the malware would worm its way onto other computers on the local network using an exploit in the SMB file sharing stack (which orignally came from leaked NSA malware). Then it would encrypt the user's files and demand the ransom.