Invasion of Privacy by Christopher Reich

This is a scary book just because it probably really could happen. Mary Grant is happily married to FBI guy Joe.  One day, he goes out to meet an informant and gets shot to death, as does the mysterious informant. The FBI is very mum about the details and Mary thinks they're hiding something. Before her husband died, he left her a voicemail with a code word indicating that something had gone horribly wrong and the only one he could trust was "Sid." Mary starts trying to investigate and soon comes up against Ian Price, a mega rich tech mogul who has big plans for taking over surveillance of pretty much all electronically transferred information in the US and the world.

Mary's only ally is a hard-drinking, out-of-work reporter, who also thinks there's something fishy about Joe's death. The closer they get to the truth, the more Ian and his minions retaliate--taking over Mary's bank accounts, phone, computers. It's a gripping story and I couldn't put it down.