According to the Wall Street Journal, the NSA has been assembling a vast database that sweeps up "transactional" data from American's emails, phone calls and other electronic communications to search for "suspicious" patterns:

According to current and former intelligence officials, the spy agency now monitors huge volumes of records of domestic emails and Internet searches as well as bank transfers, credit-card transactions, travel and telephone records. The NSA receives this so-called "transactional" data from other agencies or private companies, and its sophisticated software programs analyze the various transactions for suspicious patterns. Then they spit out leads to be explored by counterterrorism programs across the U.S. government, such as the NSA's own Terrorist Surveillance Program, formed to intercept phone calls and emails between the U.S. and overseas without a judge's approval when a link to al Qaeda is suspected.

TPM Muckraker explains that this program is substantially similar to an earlier FBI program "Total Information Awareness" (TIA):

Gorman describes the NSA's effort (elements of which have been reported before) as basically a resurrection of the Pentagon's Total Information Awareness program, which of course was de-funded by Congress once the details became public. This time around, of course, the details have remained secret. Although the budget for the NSA's driftnet is classified, Gorman cites one official as estimating it at $1 billion. One wonders what the reaction will be this time around.

The ACLU raised many important objections to the Total Information Awareness spying program, which resulted in its de-funding. You can read about the fight to kill TIA (and the many privacy and safety concerns it raised) here. We'll keep you updated as more information surfaces about this newer "Son of Total Information Awareness" program.