Security firms reported finding the code in Wednesday. The exploit code for previously unknown flaws means hackers could use the code to pounce on computer systems where managers are slow to apply patches.

"Microsoft is aware that detailed exploit code was published on the Internet for some of the vulnerabilities," the software maker said in a statement. "With the exception of MS06-027 (the Word malware that began circulating last month), Microsoft is not currently aware of any active attacks utilizing this exploit code...the exploit code does not affect users who have installed all June security updates."

In all, Microsoft issued patches for 21 flaws in its security update, saying all but two of them could let an intruder run malicious code on a compromised computer.

Some of the exploits that appear on the Web are for "critical" flaws in Windows Media Player and for "routing and remote access." The SANS Internet Storm Center reported that two exploits were for the "routing and remote access."

Verisign's iDefense team also announced that it had developed a "proof of concept" exploit code for a security hole in the ".ART" file, a file type used often for AOL services and Web sites, according to iDefense.