I missed this and hat tip to FP Blog citing a WSJ article:http://online.wsj.com/article/SB1000...googlenews_wsj

Which opens with:
An Islamic militant group affiliated with al Qaeda said it attacked a Japanese-owned oil tanker while it traveled through the Strait of Hormuz last week, adding another twist in the mysterious incident and raising fresh worry about the vulnerability of the important oil-supply route.

(Later)Privately, U.S. officials have expressed skepticism about the al Qaeda-affiliated group's claim of responsibility. They say that while the investigation isn't finished, the visible damage to the tanker hull is more consistent with a collision than a terrorist attack.
There is a 2008 thread on the Straits of Hormuz and the Iranian small boats threat. This is possibly different and IIRC the last seaborne attack on a tanker was the French-owned Limburg in the Gulf of Aden, in 2002. Background:http://en.wikipedia.org/wiki/Bombing_of_the_Limburg

For a long time the Straits of Hormuz have been a recognised choke point, with jurisdiction shared between Iran and Oman; with many navies having a presence.