Anyone providing services on the internet should check their terms of service to ensure that the terms of service aren’t amendable at any time. This is especially true after last year’s court ruling that the Zappos’ user agreement was not valid because it could be changed at any time. This makes the terms of service an “illusory promise” between the parties. It’s sort of like saying “I’ll paint your house for $200, although I may change that price at any time.” Not especially fair.
If you need to change your terms of service, make sure your users know. Give them advance notice. Make them check a box indicating they agree to the change. Courts know that users don’t just go cruising through the terms of service every couple of weeks to look for changes. You can see an example of this in Google’s Terms of Service:
Changes will not apply retrospectively and will become effective no earlier than fourteen days after they are posted. However, changes addressing new functions for a Service or changes made for legal reasons will be effective immediately. If you do not agree to the modified terms for a Service, you should discontinue your use of that Service.
That’s still a little wishy-washy (what are “legal reasons”?), but the two week notice is there to prevent it from being illusory. Another protection would be to say that you will email users when there are changes to the terms of service. Google did that too; when they had a major change in March 2012, I feel like they must have informed me in about seventeen different ways — email, and notification on login to each of their services. I just received a TOS update to Google’s AdSense product, which gives 30 days notice and requires acceptance in the user’s account or else the services are suspended. And so long as you are going to implement those good practices (you are, right?), you might as well indicate it in your TOS so that it’s clear to the judge if there is ever a dispute.
Equally important is to have your users click through the agreement, or otherwise make some active action indicating assent. Just browsing the website isn’t enough — as Eric Goldman put it (see link above), “I don’t use the term browsewrap; instead, I prefer to call those documents ‘not a contract.'”
“Change” by Nana B Agyei, cc-by license, source.