Petya (a.k.a NotPetya) is another ransom-ware file-encrypting virus worm. The latest big thing.

Apparently it spreads through the same mechanism as the WannaCry virus (NHS cyber attack May 2017), but there are also reports of it being sent through emails.
That method of spreading from one computer to another was due to a security flaw in Microsoft Windows. The code to exploit this flaw, which the US government found years ago but kept to themselves, had been called EternalBlue. A patch/fix for this was released by Microsoft in March 2017, and also included in subsequent update roll-ups.

During the NHS cyber attack crisis, I took steps to ensure that all client’s computer had this and other important updates installed. For this reason, you are already patched against EternalBlue, however you must still be vigilant with regard to opening email attachments.

As it happens, security researchers have discovered a sort of ‘vaccine’, however it will only work for the current outbreak. If the virus does get to your computer, perhaps through the opening of an email attachment, it first checks whether some other files are present on the computer, and if they are, then the virus shuts itself down and does no harm. So this is sort of like a kill switch.

I have sent a popup message to your computer to let you know that these vaccine files have been put in place on your computer, as well as to explain the patch situation above.