Updated An Avast software update pushed out on Wednesday is preventing web access for at least some devices running the firm's freebie anti-malware software.

Users affected by the problem have started threads (here and here among others) on Avast's support forum.

El Reg learnt of the issue through reader Michael S.

"Non tech savvy users will have issues reporting or getting the problem fixed," he explained. "To regain web access you have to disable Web Shield or disable Avast or uninstall Avast. To fix the issue you have to do a clean install of the latest version of software."

It's unclear how widespread the problem is. Avast's PR reps have acknowledged our requests for comment but are yet to supply a substantive response.

All HTTP requests are blocked from all applications including Windows Update. "TCP connections are established but no HTTP request is sent," according to Michael S.

False positives of one sort or another are a well-known shortcoming of security software packages, almost all of which rely on signature updates to some extent. Consequent problems are worse when either a core Windows component is flagged as potentially malign or core functionality is disabled, as in the latest case.

Avast has form for this sort of thing, if you look back far enough. An Avast update pushed out six years ago classified the whole web as malign, as we reported at the time. ®

Updated at 9am on 15 May to add: Avast got in touch late on Friday acknowledge the problem and say that a fix for Avast and AVG 17.4 has been released, alongside a guide on how to download it. Both are being publicised through Avast's user support forums.