"We hack everyone everywhere," he said.

Former officials don't appear to contradict him. Ex-NSA chief Michael Hayden described it as "commuting to where the information is stored and extracting the information from the adversaries' network." In a recent interview with Bloomberg Businessweek, he boasted that "we are the best at doing it. Period."

Malicious software used by hackers can be extremely hard to spot. But installing an antivirus program, avoiding attachments, frequently changing passwords, dodging suspicious websites, creating a firewall, and always making sure your software is up to date is a good start.

Disadvantages: Keeping abreast of all the latest updates and warily scanning emails for viruses can be exhausting.

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