Microsoft's Internet Explorer browser is coming under renewed attack by cybercriminakls seeking to take advantage of an unpatched vulnerability.
Attackers are using fake antivirus products to open back doors on victim's computers.
Microsoft first warned of the bug on March 9, saying that it had been used in "targeted attacks". But now, according to researchers, the exploits are much more widespread. By late last week, security vendor AVG was getting reports of 30,000 attacks per day, according to Roger Thompson, AVG's chief research officer.
"It's not a massive attack, but it's an unpatched exploit being used aggressively," he said Tuesday.
It appears that two separate cybergangs have begun using the exploit - the first uses it to install fake antivirus software on victim's computers; the second group is installing a variant of the Sinowal Trojan, Thompson said.
Most of the attacks are being hosted on websites that appear to be specifically set up to host the attack code, rather than hacked sites, Thompson said.
Although AVG tracked just 16,000 attacks on Monday, Thompson predicted that problem would get worse in the next few days, putting pressure on Microsoft to rush out a fix for the bug ahead of it's scheduled April 13 security updates. "I would expect it to be adopted by more gangs over the next couple of weeks, as soon as they figure out where to find a copy," Thompson said.
Rival AV vendor Trend Micro agreed that attacks are on the rise. "It's popping up all over the place," said Paul Ferguson, a researcher with the company. "It started off slowly, but I really started noticing it yesterday, and then today - there were a bunch of sites which harboured this exploit," he said.
Internet Explorer versions 6 and 7 are vulnerable to the attack. For it to work, however, the victim has to first visit a website hosting the malicious code.
Microsoft could not immediately be reached for comment on this story.