No

A cyber attack is a cyber operation, whether offensive or defensive, that is reasonably expected to cause injury or death to persons or damage or destruction to objects.

Michael Schmitt et al; Tallinn Manual 1.0, pp 92
  • Cyber Operation?
  • Expected to cause death or injury to people or damage to objects?
A Web Skimmer on The Principality of Sealand’s Online Store does not match this definition. Here's a list of actual cyberattacks and and why this matters.

What happened?

A cybercrime group hijacked the website of the Principality of Sealand, a fake nation in the North Sea, and planted a web skimmer on its online store to steal card details for people buying nobility titles (baron, count, etc).