The difference between “though” and “although”

Which is correct?
A botnet is a group of computers organized to distribute spam or malware — _________ the owners are typically unaware of the fact.

a. though
b. although
c. even though

Explanation:
The meanings of a. and b. are the same, in this context, and although though isn’t wrong, it’s less acceptable in formal writing. Even though expresses a stronger contrast between the ideas in the first of the sentence and the last, so arguably that’s the best choice.

Grammarist provides examples of when though means the same thing as although and when it doesn’t:

Examples

In these examples, although and though are the same:

Growth in Europe is maintaining momentum, although the risks related to peripheral economies have increased. [Globe and Mail]

Unlike the other comparisons, however, this one is apt, though perhaps not in a way Cantor intended. [Washington Post]

Although the birds are just a small part of his business, carefully raising the pheasants from delicate eggs to beautifully feathered birds is clearly a passion. [The Age]

Some grown unschoolers, though positive about it overall, admit they’ve at times longed to be just like the other kids … [National Post]

And in these examples, though is an adverb and hence not interchangeable with although:

             This weekend, though, theaters were packed. [Los Angeles Times]

             There was another twist to come, though, as Pavlyuchenkova defied her flagging

Even though Grammarist seems to disagree, though doesn’t seem acceptable to me in formal writing. I always change it, when editing. What do you think?

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