Half of breached firms say they were compromised due to a vulnerability for which a patch was available but not applied.

Attackers use the approach to look like legitimate traffic and hide data exfiltration in plain sight.

Discount brokerage firm Scottrade began firing off emails late last week, warning customers that as a result of a breach, their names and street addresses may have been stolen from its system. Scottrade’s statement on the incident, published on its site last Thursday doesn’t exactly rule out that more sensitive information, such as users’ Social Security...