The NSA and its U.K. counterpart, GCHQ, use a tool called QUANTUMINSERT to tracks a person's internet browsing and at opportune moments direct the user's computer to one of its FOXACID exploitation servers.
One document showed that QUANTUMINSERT was most effective when people were trying to visit the professional networking site LinkedIn, Der Spiegel said. The success rate was more than 50 percent, it said.
The NSA could not be immediately reached for comment Sunday night.
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