C- The quarterly external scans

The point of sale (POS) environment refers to a transaction that takes place at a merchant location (i.e. retail store, restaurant, hotel, gas station, convenience store, etc.). An Internet protocol (IP) -based POS is when transactions are stored, processed, or transmitted on IP-based systems or systems communicating via TCP/IP.
PA-DSS refers to Payment Application Data Security Standard maintained by the PCI Security Standards Council. PABP is Visa’s Payment Application Best Practices, which is now referred to as PA-DSS. Visa started the program and it is being transitioned to the PCI Security Standards Council (PCI SSC). To address the critical issue of payment application security, in 2005 Visa created the Payment Application Best Practices (PABP) requirements to ensure vendors provide products which support merchants' efforts to maintain PCI DSS compliance and eliminate the storage of sensitive cardholder data. See www.visa.com/pabp for more information. The Payment Card Industry Security Standards Council (PCI SSC) will maintain the PA-DSS and administer a program to validate payment applications' compliance against this standard. The PCI SSC now publishes and maintains a list of PA-DSS validated applications. See https://www.pcisecuritystandards.org/security_standards/pa_dss.shtml for more information. VISA MANDATE PHASE DEADLINE

1. New PCI Level 4 merchants (including new locations of existing relationships) may not use vulnerable payment application versions – those that store prohibited cardholder data. January 1, 2008 2. New PCI Level 4 merchants using third-party payment software must be either PCI DSS-compliant or use PA-DSS validated compliant payment applications. October 1, 2008 3. ALL PCI Level 4 merchants (new and existing) using third-party software must use validated applications. July 1, 2010
PCI DSS requirement 3.3 states "Mask PAN when displayed (the first six and last four digits are the maximum number of digits to be displayed).” While the requirement does not prohibit printing of the full card number or expiry date on receipts (either the merchant copy or the consumer copy), please note that PCI DSS does not override any other laws that legislate what can be printed on receipts (such as the U.S. Fair and Accurate Credit Transactions Act (FACTA) or any other applicable laws). See the italicized note under PCI DSS requirement 3.3 “Note: This requirement does not apply to employees and other parties with a specific need to see the full PAN, nor does the requirement supersede stricter requirements in place for displays of cardholder data (for example, for point of sale (POS) receipts).” Any paper receipts stored by merchants must adhere to the PCI DSS, especially requirement 9 regarding physical security.
If you electronically store cardholder data post authorization or if your processing systems have any internet connectivity, a quarterly scan by a PCI SSC Approved Scanning Vendor (ASV) is required.
A network security scan involves an automated tool that checks a merchant or service provider's systems for vulnerabilities. The tool will conduct a non-intrusive scan to remotely review networks and Web applications based on the external-facing Internet protocol (IP) addresses provided by the merchant or service provider. The scan will identify vulnerabilities in operating systems, services, and devices that could be used by hackers to target the company's private network. As provided by an Approved Scanning Vendors (ASV’s) such as ControlScan the tool will not require the merchant or service provider to install any software on their systems, and no denial-of-service attacks will be performed. Note, typically only merchants with external facing IP address are required to have passing quarterly scans to validate PCI compliance. This is usually merchants completing the SAQ C or D version.
Every 90 days/once per quarter you are required to submit a passing scan. Merchants and service providers should submit compliance documentation (successful scan reports) according to the timetable determined by their acquirer. Scans must be conducted by a PCI SSC Approved Scanning Vendor (ASV). ControlScan is a PCI Approved Scanning Vendor.
PCI is not, in itself, a law. The standard was created by the major card brands such as Visa, MasterCard, Discover, AMEX, and JCB. At their acquirers/service providers discretion, merchants that do not comply with PCI DSS may be subject to fines, card replacement costs, costly forensic audits, brand damage, etc., should a breach event occur. For a little upfront effort and cost to comply with PCI, you greatly help reduce your risk from facing these extremely unpleasant and costly consequences.
Source : GIE-CB