Various ESTA’s have been revoked

There have been several already approved ESTA’s withdrawn by the United States Department of Homeland. 

Security

We had already noticed that America was sharpening the safety requirements. But now it appears that already approved ESTA’s (Electronic System for Travel Authorisations) have been withdrawn by the United States Department of Homeland Security. This is due to the changes in their policies. It is mainly about persons who have previously travelled to or have a second nationality of Iraq, Iran, Sudan or Syria.
The following travellers will no longer be eligible to travel to America or be admitted to America according to the Visa Waiver Programme (VWP): persons living in countries falling under the VWP who have visited Iraq, Iran, Sudan or Syria on or after 1 March 2011. (Exceptions allowed)

Of course, these restrictions do not apply to travellers who fall under the VWP who have visited one of these countries due to military service or government work. Travellers falling into one of the above categories, whether visiting Iraq, Iran, Sudan or Syria on or after 1 March 2011, or having a second nationality from one of these countries have received an email on January 21, 2016 concerning their revoked ESTA.
The Customs and Border Protection (CBP) is working hard to inform all travellers who fall into one of the above categories as soon as possible. Travellers who have now been informed of the fact that they are no longer eligible to travel to the US via VWP may still apply for a non-immigration Visa at the U.S. Embassy or Consulate.

This new law cannot prohibit these travellers from entering the US with a valid Visa. Please note that requesting a non-immigration Visa lasts longer than applying for an ESTA. This may take several weeks. The Foreign Affairs Department is also willing to use additional staff to assist the embassies and consulates with the additional non-immigration Visa applications that will come in. This new law also requires all VWP travellers to use an electronic passport to travel to the US. They are also working on improving the information exchange of terrorism and criminal data. For example, they use Interpol databases and screen travellers better before entering the U.S. The vast majority of travellers covered by the VWP will not further interfere with these new measures.

Source: cbp.gov