Microsoft Excel users were warned of a new flaw that allows remote hackers to run malicious code on an unsuspecting user's computer, Infopackets.com reported.

Users of Microsoft Office Excel 2007, or those using any .XLS files would be asked through e-mail to open a spread sheet. Once that happens, two files — one valid, the other infected, will execute a hidden Trojan horse downloader, Inforpackets.com reported.

The downloader can be used by hackers to log personal data and user keystrokes.

Infopacket.com reported because one valid document is also used, it will be difficult to detect the attack.

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