A Dutch police unit has confirmed to the BBC that it can decrypt messages on Blackberry's most secure smartphones.
It did not go into details about how it does this but said that its methods allow police to read messages.
Troubled phonemaker Blackberry has prided itself on providing customers with one of the safest methods of communication.
In response to the news, it said it could not comment without more information about the crack.
"We are confident that Blackberry provides the world's most secure communications platform to government, military and enterprise customers.
"However, we can't comment on this claim as we don't have any details on the specific device or the way that it was configured, managed or otherwise protected, nor do we have details on the nature of the communications that are claimed to have been decrypted," a spokeswoman told the BBC.
It is believed that the tests were conducted on PGP Blackberrys, handsets with an extra layer of encryption provided by online vendors, such as GhostPGP and TopPGP.
The Netherlands Forensic Institute (NFI), a body that provides forensic evidence to Dutch police, was unwilling to provide details on how it decrypted messages from the devices, although it seems that it does need physical access to handsets.
Technology website Motherboard reported that it uses a piece of forensic software made by Cellebrite. Others speculated that the NFI may have removed a memory chip and dumped the data from it.
The NFI could not decrypt all messages. According to Dutch blog Crime News, which first reported the news, 275 out of 325 encrypted emails were cracked.
So-called PGP Blackberrys are advertised as being particularly suited to people wanting to keep data secure and have been linked to criminals in the past.
GhostPGP said that its services had not been compromised.
In 2014, it was reported that such phones were used by those involved in a series of killings in Australia. The Sydney Morning Herald claimed that police officers had travelled to Blackberry headquarters looking for advice on how to access encrypted data on the phones.