HP has fixed flaws in a patch-management program bundled with its computers, printers and other hardware that could be used by hackers to 'brick' HP or Compaq PCs.

In an alert sent to customers who subscribe to its security warning service, HP said users should run Software Update to patch the flaws disclosed last week by a Polish researcher known only by his alias, 'porkythepig'. A pair of bugs in the update service's ActiveX control can be used to execute remote code or gain additional access rights, porkythepig said then. He also posted proof-of-concept exploit code that showed how to use one of the vulnerabilities to overwrite and corrupt crucial Windows' system files, an attack that would leave any affected PC unbootable.

That would essentially 'brick' the system, since many HP and Compaq PCs do not include a restore CD or DVD, but instead place operating system and application restore files on the hard drive. (Those with separate restore media could likely be restarted.)

HP's advisory on Friday instructed users to run Software Update on any machine that has the application, even if the update service is never used. Running Update presumably disables the flawed ActiveX control by setting its 'kill bit' in the Windows registry - the fix suggested last week by Symantec before HP owned up to the problem - although that could not be verified today.

Danish vulnerability tracker Secunia ASP pegged the Software Update issue as 'highly critical', its second-most-dire threat ranking, but HP, which does not rate vulnerabilities, only noted that the advisory "should be acted upon as soon as possible".

HP also acknowledged that the buggy Software Update was in even wider distribution than first thought. Last week, porkythepig speculated that the newest vulnerabilities might affect the same 83 laptop models that had been hit with other bugs on December 12. HP, however, said in the advisory that the application "may be installed on a PC as part of the software supplied with certain HP PCs, printers, scanners, or cameras".

Customers who don't receive the company's security alerts via e-mail can read the HP advisory on the Bugtraq security mailing list, where the alert was also posted last Friday.

HP did not respond to a request for comment on Monday.