There is an unapatched vulnerability in Internet Explorer (all versions) and you are running a risk of having a malicious file being downloaded and executed without warning.
How to protect yourself?
If you are using Windows XP, it is safest to use another browser until there is a patch. Although now it is mainly Chinese sites that are getting hacked and injected with malicious code, it could spread.
Microsoft has an advisory here, with some advice how to protect yourself.
NIS is detecting at least some versions of this, which I have checked myself. With Internet Explorer. 
How did I dare? (I wouldn't advise you to do the same though!)
If you are using Windows Vista, like me, there are several steps you can take to harden your IE against this and other threats. Enable Data Execution Prevention for all programs and services, enable Protected Mode in Internet Explorer and finally enable the option to Enable memory protection to help mitigate online attacks.
Run Internet Explorer as an Administrator. To enable DEP, perform the following steps:
1. In Internet Explorer, click Tools, click Internet Options, and then click Advanced.
2. Click Enable memory protection to help mitigate online attacks.
Which brings me to a final point, which is one of the two reasons I am opening this thread.. If you do this last option, Internet Explorer would crash in most cases. The culprit? Almost certainly, Google Toolbar (that is if you have it, most people do)!
The toolbar in Mozilla Firefox is compatible with Data Execution Prevention. The one in IE, however, is not. Why on earth is Google practically sabotaging an option that makes IE7 safer? I uninstalled the toolbar, of course. In protest. And now my IE 7 doesn't crash.
The Norton toolbar is, needless to say, compatible on both browsers.
If you are not technically savy and you don't feel like doing all this, of course, the easiest thing to do is not to browse with IE for a while.