Microsoft on Saturday said it was working with law enforcement to track down those responsible for an attack that compromised enterprise web sites running unpatched versions of IIS 5.0 (Internet Information Services).
The server that was the source of the attack, called Download.Ject, was tracked down in Russia and shut down Thursday, according to Microsoft.
But the software giant said it was not aware of "any widespread customer impact" from Dowload.Ject, which it said was not a worm or virus but a "targeted manual attack by individuals or entities towards a specific server."
The attack exploited a vulnerability in Internet Explorer in order to send malicious code to visitors of compromised web sites.
Microsoft advised customers to install the update it issued in April and said Internet Explorer users should use high security settings.