One of the easiest tools to use is the WayBack Machine from the Internet Archive. The Internet Archive Wayback Machine is a service that allows people to visit archived versions of Web sites. Visitors to the Wayback Machine can type in a URL, select a date range, and then begin surfing on an archived version of the Web. Imagine surfing circa 1999 and looking at all the Y2K hype, or revisiting an older version of your favorite Web site. The Internet Archive Wayback Machine can make all of this possible.

How can this be used for due dilligence?

The Wayback Machine has been archiving websites since 1996. If a website claims to be in existance for a few years you can check if there is an archived version of that website available. If there is you can check all sorts of information, like contact data. Is the address still the same, or is the website very different from the current website? In that case they might have just bought the domain name and make false claims about their history.

What you basically do is compare the archived website with a current website. Check for differences in email addresses, postal addresses, names, document names, links to other websites, terms of service etc.

To get an idea of how you use the Wayback Machine see my review on AMF1989.

A few things you should know about archived websites

Not all websites are archived. Most of its data comes from Alexa. If you want your website listed in the Wayback Machine you should get a listing with Alexa. To get a listing with Alexa you best get a listing in the Open Directory Project.

It generally takes 6 months or more for pages to appear in the Wayback Machine after they are collected, because of delays in transferring material to long-term storage and indexing.

You can find the Wayback machine here:
http://www.archive.org