The hackers' collective, calling itself The Binary Guardians, targeted the portals for the government, the supreme court and the legislature, among others.
The sites for private companies were also affected, including subscription TV service DirecTV and telephone provider Digital.
The online operation came a day after three military officers -- a dismissed captain and two lieutenants -- led around 20 men in uniform on a raid of an army base in the city of Valencia.
Several of the hacked sites were offline late yesterday.
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Those for President Nicolas Maduro's office and for the electoral council were eventually back to normal.
The Binary Guardians showed on Twitter the screen they had inserted on the portals' home pages: a tract supporting the rebel group's "Operation David" on the army base, next to an excerpt from Charlie Chaplin's movie "The Great Dictator."
"Our struggle is digital," the hacker group said. "You close the streets, we do so to networks."