Microsoft customers could not gain access to many of the company's Web sites, including Microsoft.com and MSN.com, on 24 and 25 January, following denial of service attacks against routers at a company datacentre.
Following the first of these attacks Microsoft issued a statement that it had informed the FBI and had "taken immediate steps to make sure that our networks have improved protection from this type of attack".
The second attack followed less than 24 hours later. This time Microsoft said in a longer statement that, "We did not apply sufficient self-defence techniques to our use of third-party products at the front-end of parts of our core network infrastructure."
Both attacks came hot on the heels of self-inflicted denial of Microsoft Web site services on 23 and 24 January.
These outages were the result of an error in a configuration change by a technician to routers on the edge of Microsoft's DNS network. DNS servers hold addressing information for Web sites and the configuration error caused a breakdown in communication to many Microsoft servers.
Graham Titterington, senior analyst at Ovum, said, "Businesses need to configure built-in redundancy. They need to be operating in parallel rather than in series and not presenting single points of failure in their networks.
"Ultimately it is a question of whether the cost of extra equipment is worth paying to defend against a one- or two-hour outage."
Highlighting the threat to routers, Titterington said, "If the object of the exercise is denial-of-service rather than the clearly political defacing of Web sites, then routers are a much more productive device to target."
The company has been the victim of numerous malicious attacks over recent months. In December the Slovenian Web site was defaced twice in three days, and in October the company admitted that source code for some developmental products had been seen by intruders.