According to Sunnyvale, Calif.-based Fortinet, the exploit -- dubbed "JS/CreateTextRange.B" to differentiate it from the original -- takes much less time to execute.
"In this version, the time to wait before the execution of the payload (aka hacker's code and potentially damaging payload) is minimized," said Fortinet's alert.
The change could be significant, since the one exploit now in circulation takes 5 to 10 seconds to execute, said Dan Hubbard, senior director of security and research at Websense.
"Some people give up and close their browser before that finishes," he said. The relatively long time for exploitation, he said, is in contrast to the Windows Metafile attack earlier in the year. "In that, as soon as you hit a page, you were infected," he said.
Speeding up the infection could cause fewer users to close IE, and lead to more machines falling under the sway of spyware and keyloggers.
As of mid-afternoon Friday, Microsoft had not pushed out a patch for the IE flaw, but users had other options to defend themselves, including disabling the browser's Active Scripting feature, installing one of two third-party fixes, or switching to another Web browser, such as Firefox.