Other researchers, meanwhile, said that the timing of the attacks, which have already started, was not coincidental.

"The updates Microsoft released yesterday do not address this possible vulnerability," a Microsoft spokesman said today in an e-mail reply to questions, "but I can tell you that Microsoft is investigating these new public claims of a possible vulnerability in Internet Explorer."

Exploit code, which , is actively seeking out victims, according to security researchers there and in the U.S. Those researchers have found attack code on multiple malicious domains and servers. Elsewhere today, an exploit was posted to the milw0rm.com site, a popular destination for public posting.

Symantec Corp. echoed Microsoft today, confirming that the flaw was not fixed by , which included four patches, all judged "critical," for IE.

"The attack works successfully against a fully patched Windows XP SP3 with Internet Explorer 7, including all recent Microsoft Tuesday patches," said researcher Elia Florio in an entry to the . "Also, Internet Explorer 6 could potentially be affected by the same problem and is therefore only temporarily immune to this initial exploit, which seems to target Internet Explorer 7 on Windows XP and 2003 systems."