Microsoft plans to release seven software patches next week. Four of the updates will fix bugs in Windows while another three will address flaws in Microsoft Office. Both sets of patches will address critical flaws, which attackers could exploit to run unauthorised code on a PC without any user action.

The new software will likely fix a number of publicly reported vulnerabilities in Office, some of which concern Excel, said Gunter Ollmann, director of Internet Security Systems' X-Force threat analysis service.

Last month, Microsoft confirmed that it was investigating three issues that relate to Office, following reports that hackers had launched a targeted attack, against an unnamed government contractor, that took advantage of a bug in its Excel spreadsheet software.

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 unauthorised ActiveX control, Microsoft said.

On Thursday another bug was added to the mix with security vendor Secunia warning of a flaw affecting Asian language versions of Excel. As with the other bugs, victims would need to be tricked into doing a little work before compromising their systems, but if this were to happen, attackers could run their malicious software on the PC, Secunia said.

The seven patches may keep system administrators busy next week, but not as busy as they were in June. Last month Microsoft released 12 security updates.