Most ToS state that their terms are subject to change. I do not know whether or not a company has to explicitly state that the terms provided are perpetual, but

Most ToS state that their terms are subject to change. I do not know whether or not a company has to explicitly state that the terms provided are perpetual, but there are lots of examples of companies changing their ToS retroactively. For example: http://arstechnica.com/tech-policy/2008/09/google-on-chrome-eula-controversy-our-bad-well-change-it/ http://arstechnica.com/tech-policy/2008/09/google-on-chrome-... http://boardingarea.com/viewfromthewing/2012/10/10/united-makes-another-retroactive-change-to-bonus-terms-and-conditions/ http://boardingarea.com/viewfromthewing/2012/10/10/united-ma... And here is an interesting paper about retroactive lawmaking by the government: http://www.law.harvard.edu/students/orgs/jlpp/Vol30_No2_Weienonline.pdf http://www.law.harvard.edu/students/orgs/jlpp/Vol30_No2_Weie...