Another warning has been issued over data-stealing malware that exploits a vulnerability in Internet Explorer.
Although the threat from last week's "download.ject" attack has subsided, malware authors have not missed a beat in their efforts to use flaws in Internet Explorer as a gateway to steal banking and credit card information.
The malware, which has been identified by the SANS Institute, is delivered to users' PCs through pop-up windows that appear when users log on to financial portals.
It seems that the suspect pop-ups are delivered on certain websites that run ads from third-party ad servers, which appear to have been hacked. When the pop-ups appear, vulnerable versions of Internet Explorer begin downloading a malicious file that records activity - such as passwords - onto the infected PC and sends that data to a server reportedly located in Estonia.
Some 50 financial institutions have been affected, reports claim, and a patch for the exploit used by the as-yet-unnamed malware has not been released.
The latest trouble is sure to add to the pressure Microsoft is facing with Internet Explorer. The new warning comes less than a week after it was discovered that a number of websites running Microsoft's Internet Information Server 5.0. had been hacked.
The attackers then dropped code onto the compromised servers which exploited a vulnerability in Internet Explorer. This installed Trojan horses and keyloggers on the computers via IE to the visitors of the compromised sites.
Microsoft is said to be working feverishly to deliver patches for these "zero-day" bugs, and there is now speculation that the company has decided to rebuild Internet Explorer from the ground up in order to ensure that the software is air-tight.
Meanwhile, US-CERT is telling users to deactivate certain advanced functions in Internet Explorer, such as ActiveX, to help prevent infection from a whole range of viruses and Trojans. Deactivation of these higher functions is not a cure-all and could impact on the functionality of some sites, experts say.
An even safer route would be to switch to a rival Internet browser like Netscape, Safari, Opera or Mozilla.