Wednesday, the company .

Although other researchers continue to claim that thousands of , then used to serve "drive-by" attacks against unpatched browsers, Marcus wasn't certain about the numbers he's seen bandied about. "But absolutely, there's been a lot of activity around this," he said. "A lot of the bad guys have embedded IFRAMES in their sites to attack IE."

According to other reports, the IE exploit has been added to one or more multi-strike hacker toolkits that try several different exploits when users visit a compromised or malicious site. "If it's not in one of those yet, it probably will be," said Marcus. "Some of the exploits in those kits are years old, so a good one like this, unpatched until yesterday, will make its way into them."

Marcus recommended that users be cautious about opening Word documents, keep their security software up-to-date, and apply the IE patch as soon as possible.