"Computers whose software is not up to date are specifically exposed to Angler attacks, which are known as drive-by downloads. If any of the exploits is successful, CryptoWall 4 is deployed on the computer."
"Because of the mechanisms involved and the attackers’ objectives, the campaign is prone to achieve large distribution and affect a big number of PCs and their users." (Quoted from the interesting blog post linked to in the last paragraph)