scary: maybe.
expensive: well the information is free.
I will attempt to explain it in a non-scary fashion.
Hard drives (at least the ones that aren't SSDs) consist of rotating platters of magnetic media.
Each platter is divided into several thousand different regions (
wikipedia link) that are the smallest unit that can be read or written to at a time.
If something happens to the physical media in a sector (solar radiation, loss of magnetic charge, manufacturing defect, etc) that prevents the drive from correctly reading the sector you get file corruption.
Most of the time you don't even notice when a sector is going bad, because the problem gets recognized before the sector is beyond recovery. The drive will read the data off the sector, flag the failing sector as bad, and write the data into a free sector (a percentage of the drives total space is reserved for just this occurrence). This happens all within the drive itself, totally independent of the OS.
As people demand more storage in the same physical space, the size of sectors has to shrink. And the rotational speed is also probably increasing as well. Which means it takes less going wrong before the drive has problems reading/writing to a specific sector.
The best tool I have found for failing hard drives is
spinrite. It is the only tool I know of that will perform statistical analysis on problem sectors in an attempt to recover the data. At $90, it's not cheap. But I have personally seen it take laptops from non-booting to fully-functional.
But given that I have no guarantee that a spinrite could solve your problem (or even that corrupt sector caused this problem), I'm not going to tell you that you need to buy it.
I doubt that it was caused by a virus, as the motivation for writing them now is harvesting personal info. Making computers not boot doesn't get them any money, stealing your banking details or turning your computer into a zombie does.
(hopefully this has helped, and not just added more confusion)
-Terry
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"so listen up boy, or pornography starring your mother will be the second worst thing to happen to you today"
TF2: Spy