Today, despite widely available technology ....

[singhpk2]

Today, despite widely available technology such as high-resolution scanners and printers, counterfeiting is more difficult than it was at the time of the Civil War, when it was estimated that one-third of all currency in circulation was counterfeit.

This sentence is stated as correct as it is.
My question:
Where is the antecedant of the second it (....when it was estimated that ....)?

Please clarify.

Question source: MGMAT Test

[esledge]

In the future, please also post the answer choices for the benefit of other users.

The antecedent of the second "it" is "counterfeiting":
Today, ...., counterfeiting is more difficult than it was at the time of the Civil War...

Note the parallelism between "counterfeiting is" and "it (counterfeiting) was." The comparison signal "more difficult than" indicates the need for parallelism, both in terms of logic (counterfeiting, now and then) and structure (both noun and pronoun are the subject of their respective verbs).