The action comes as Redmond, Wash.-based Microsoft suffers its third day of widespread outages, including problems at its flagship portal MSN.com, travel site Expedia, free e-mail service Hotmail and WindowsMedia.com. The company issued a statement late Thursday saying it was the target of a denial-of-service attack earlier in the day against the routers that direct traffic to the company's Web sites.
A Microsoft representative said the IE 5.5 service pack update was unrelated to the outages.
The company would not disclose what is amiss with the software, saying only that the update will not add new features to the service pack, nor will it eliminate any software bugs.
"It's not routine; they just realized they had to update a couple specific areas," the representative said.
As of Thursday afternoon, visitors to the IE 5.5 download site were greeted with the following message: "Internet Explorer 5.5 and Internet Tools Service Pack 1 is temporarily unavailable. Very shortly, this version of Internet Explorer will again be available from this location."
The Internet Explorer home page does allow visitors to download IE 5.01, the browser's previous version.