UK secret services say that the encrypted files Edward Snowden held from his time working at the NSA have been accessed by intelligence agencies in China and Russia.
The Sunday Times reports that the top secret files have been hacked meaning that British and American spies could be identified and located.
Wanted by US authorities, Snowden has been in hiding for some time now. It is believed that the time he spent seeking refuge in Hong Kong and Moscow may have given security official the opportunity to access the data he held.
Although the data was protected, it is thought that the encryption was hacked, and US and UK intelligence services have been "forced to intervene and lift their agents from operations to prevent them from being identified and killed".
The Sunday Times quotes a number of people - who chose to remain anonymous - who say that the documents would enable enemies to identify spies and agents because of the information they contain and the techniques they reveal. It is feared that the potential for gaining access to the Snowden's data is the very reason China and Russia offered him asylum.
Snowden is accused of having "blood on his hands" - a sentiment that is very much in line with those who feel he has acted treasonously. The whistleblower blew the lid off mass surveillance programs undertaken by Western governments, sparking an ongoing debate into privacy and security issues online.
The sheer volume of data Snowden leaked means that it is impossible to know everything the documents contain, but there are concerns that potentially damaging information has now fallen into the wrong hands.