Antivirus company Sophos has advised users to keep a sense of proportion and "calmly ensure all computers are correctly patched". The company said that as yet, there have not been any hackers or worms exploiting the flaws.
Graham Cluley, senior technology consultant at Sophos said: "With doom-laden headlines in the newspapers about
"This announcement couldn't have come at a worse time for Microsoft, as it tries to build its reputation for security," said Cluely.
Antivirus company TruSecure confirmed that there have so far been no incidents exploiting the security hole, which affects the way Windows handles digital certificates.
TruSecure said business should give highest priority for patching to domain controllers, Exchange servers, Internet Information Servers (IIS) which use certificates and VPN and firewall appliances that accept authenticated connections.
"Microsoft's critical network security infrastructure components must be patched immediately to ensure the on-going, and significant trust businesses place in them," said TruSecure chief scientist Russ Cooper in a statement.
