Whoever targeted the Bush family was probably not a "high-tech nation-state adversary," Wallach said. "If it were, you wouldn't see their tracks. ... It's probably somebody who thought they could make a quick buck."
Unlike the email scams known as phishing that attempt to fool users into giving up bank account information and passwords, more sophisticated attempts called spear-phishing go after specific individuals or institutions, Wallach said.
According to the FBI, spear-phishing sends legitimate-looking emails that offer plausible explanations for requesting personal data, along with a link. Clicking on the link can download malware that gives the hacker access to things like address lists.
"It's hard to know what kind of miscreant we're dealing with here," Moore said. "It could be someone trying to seek attention to show they can do it. You target a political figure, you're trying to show, 'Nobody is above what we can do.'"
Guccifer could be outside the U.S., making things more complicated for authorities in pursuit, Moore said.
"Of all the famous people to pick on," he added. "I wouldn't pick on someone who has an entire law enforcement branch dedicated to protecting them."
Associated Press writers Diana Heidgerd and Jamie Stengle in Dallas, Ted Bridis in Washington, Gary Fineout in Tallahassee, Fla., and Steve Peoples in Boston contributed to this story.
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