The Anonymous group of activist hackers took responsibility for attacks on the Web sites of Mexico's defense and navy departments.
Hackers gained access to all of the information in the defense department's computers, Anonymous said on Twitter.
The site's normal public content was also replaced by a statement on the disturbances surrounding the Dec. 1 inauguration of President Enrique Peña Nieto and an early manifesto from the Zapatista rebels, who staged a brief armed uprising in the southern state of Chiapas nearly 20 years ago.
In an initial Twitter message, the self-proclaimed Mexican Hacker Team signaled that "the grenade" would go off at 2000 GMT Wednesday.
"We are taking down Sedena (the defense department). We are hacking the entire server. We are stealing all their information," the group said in a subsequent tweet.
Sedena issued a statement hours later saying that while its Web site was temporarily down, the department's internal information and communication systems were "functioning with complete normality."
The navy department said its Web site was targeted only by a simple denial-of-service attack and that no sensitive information was compromised. EFE