For visitors under the Visa Waiver program going to US, there's a requirement to apply ESTA before traveling. Details about this program here. It is suppose to be a free process according to cbp.gov.

A reader by the name of AK wrote in and advise us that some possible scam sites are on the Internet charging a fee for people to apply to the ESTA program. No words on whether the applicants actually get the ESTA with the scam sites or if the information are stolen for other purposes.

The real website for ESTA application is  https://esta.cbp.dhs.gov/esta/esta.html   Be aware of the fake sites.

------------------------------
Jason Lam, http://twitter.com/jasonlam_sec