WikiLeaks founder Julian Assange. (Photo by Espen Moe via Flickr)

According to The Sunday Times, the encrypted documents contain information on BP and Guantanamo Bay. But the U.S. Defense Department does not know what's in the files and it is unlikely they could unencrypt them, reports The Sunday Times.

Assange also has documents on Bank of America and a U.S. airstrike in Afghanistan that killed civilians.

Sweden has issued an arrest warrant that names Assange, who is in Britain, in an alleged rape. The WikiLeaks site has also faced many issues since the release of hundreds of thousands of U.S. diplomatic cables.

Most recently, Pay Pal, which allowed WikiLeaks to collect donations through its service, blocked the site's account, saying that Pay Pal did not support the site's illegal activity.

Read more about the WikiLeaks "insurance" documents here.