The patches will be released on July 11 as part of Microsoft's regularly scheduled monthly security updates.
The new software will likely fix a number of publicly reported vulnerabilities in Office, some of which concern Excel.
Two of the bugs could be used to compromise a PC, but they would first require user action like opening a malicious document and clicking on hyperlinks. The third appears to be less critical, but it could be used to run an unauthorized ActiveX control, Microsoft said.
Another bug was added to the mix today with security vendor Secunia warning of a flaw affecting Asian-language versions of Excel. As with the other vulnerabilities, victims would need to be tricked into doing a little work before compromising their systems. But if that happened, attackers could run their malicious software on the PC, Secunia said.