One of the occasionally useful but not very well known resource on the web is related to the web itself. It’s the Internet Archive Wayback Machine.
As the name indicates, it saves snapshots of the internet content as it appeared at some times in the past. As of now, it has saved 487 billion pages. The wiki has more details, which is definitely worth a read. Where is it physically located? Wiki says:
“The Archive has data centers in three Californian cities, San Francisco, Redwood City, and Richmond. Its collection is mirrored for stability and endurance at both the Bibliotheca Alexandrina in Egypt and at another facility in Amsterdam.”
One of the features of the archive is its “Save Page Now” function. It captures a web page as it appears at a specific time for use as a trusted citation in the future. 
I use that feature every so often. I recently used it to capture a case of possible plagiarism. Following a search yesterday, I landed on this page, “Civilizations die by suicide, not by murder“. It relates to the famous British historian Arnold Toynbee’s summary statement about how civilizations perish, in his 12-volume magnum opus, “A Study of History.”
After reading that, I came across another page on the same subject, titled, “A Study of History – Arnold J. Toynbee“. This was a much longer and fuller treatment. And I realized that the previous page had plagiarized content from it. Compare the two to see what I mean.
And here’s where the Wayback Machine comes in. I have saved both pages. It establishes the plagiarism occurred even if the contents of the pages are changed. Here is the Stefan Zenker page in the WB machine and the partly copied page.
In case you are wondering, I did write to Mr Zenker and he responded. I have also written to the author of the shorter piece but have not got a reply yet.
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Life is a Random Draw 