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Warning issued on Office 365 mail vulnerability, but Microsoft denies problem

Office 365 packaging
Photo: Getty Images

Use of ECB encryption shown to leave mail vulnerable in security firm’s tests.

Cybersecurity company WithSecure has published details of a vulnerability in Microsoft Office 365 Message encryption (OME), but Microsoft is so far refusing to acknowledge there is a risk that needs addressing.

WithSecure says the problem comes from Microsoft’s decision to use a block cypher confidentiality mode called Electronic Codebook (ECB). A