I have 10 computers running freshly installed Windows 7 (SMB 1.0 protocol disabled). Only the ones having Fiddler installed are infected with ransomware (encrypting the files for a BTC ransom with email: firstname.lastname@example.org).
The first attack happened few weeks ago and yesterday again. The only external software other than Windows installed on the infected machines is Fiddler.
Please check your environment in any case, you may be infected somehow.