The publisher of the uTorrent file-sharing program has admitted to suffering a major security breach that allowed attackers to substitute downloads of its client for malware pushing fake antivirus software.

Anyone who downloaded its uTorrent program between 4.20am Pacific time (12.20pm BST) and just after 6am on 13 September will have been downloading the Security Shield scareware program, which pesters the user to pay for protection against non-existent threats it claims to have detected.

Originally, the company believed that both BitTorrent and the cut-down uTorrent clients had been affected, but a later clarification said that the former was not now thought to be involved.

"Clarification: This only affects users who downloaded software specifically from utorrent.com between the hours above this morning. Users who previously downloaded our software are not affected," said a company blog.

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