Microsoft has been slammed for disrupting four million websites following its takedown of dynamic DNS provider No-IP earlier this week.
No-IP claimed the legal seizure of 23 of its domains had led to inconvenience for millions, telling security blogger Brian Krebs that it had found only 2,000 sites distributing malware out of an alleged 18,000.
Natalie Goguen, marketing manager at No-IP, said: "They claim that their intent is to only filter out the known bad hostnames in each seized domain, while continuing to allow the good hostnames to resolve. However, this is not happening."
Microsoft admitted that innocent customers had experienced a temporary loss of service "due to a technical error", but claimed that service had been restored at 6am Pacific time, which No-IP disputes.
The computing giant criticised No-IP for not taking corrective action in the wake of "numerous reports" of domain exploits on its service, though No-IP said that Microsoft failed to approach it before the takedown.
Bob Tarzey, analyst at research firm Quocirca, said: "Microsoft is damned if it does, damned if it does not. It has taken action to protect users and hampered legitimate use in the process.
"Let's hope No-IP improves its security and Microsoft learns how to better respond next time. But, if Microsoft had done nothing the dissenters would shout as loud anyway."
Many on Twitter pointed out that Microsoft's Hotmail service has been used by criminals to spread viruses, with no similar legal action being taken against the company.
Simon Pugnet, lead programmer at Static Games, said: "Maybe somebody should ask the US courts to shut down Hotmail because some of its users use it to distribute the malware that caused this problem in the first place?"