'Ransomware' traps firms' and individuals' documents behind a complex password by a virus called Archiveus, then demands they buy goods from an online pharmacy in return for the code to unlock it.

But experts from the Sophos security company have cracked the password, which stops victims accessing all the files in their My Documents folder.

Spokesman Graham Cluley said:

"The password is deliberately long and complicated in an attempt by the hackers to avoid people easily cracking it.

"Experts at Sophos have disassembled the Archiveus Trojan and determined that the password is mf2lro8sw03ufvnsq034jfowr18f3cszc20vmw.

"So there should be no reason for anyone hit by this ransomware attack to have to make any payments to the criminals behind it."