A small update:
from this site:
http://krebsonsecurity.com/2014/01/a...usion-malware/
"The source close to the Target investigation said that at the time this POS malware was installed in Target?s environment (sometime prior to Nov. 27, 2013), none of the 40-plus commercial antivirus tools used to scan malware at virustotal.com flagged the POS malware (or any related hacking tools that were used in the intrusion) as malicious. ?They were customized to avoid detection and for use in specific environments,? the source said."
So I think whoever attacked Target was not a simple webmaster or a small group of cyber criminals. It was more a group that knew about how certain POS work , maybe a certain type and knew something about Target's security protocols..