Is it a virus??

[edwardcullensothermarriedwoman]

Almost every time I click a link on mumsnet today, another IE page opens up, I get a download window, and an error message in front of it (thanks to my Internet Security I think, phew) saying that it can't download because the site can't be accessed or isn't available. Yesterday, at random occasions it was opening a new page, then a message saying my computer was infected came up, and the internet page changed to look like "My Computer" searching and finding trojans and worms.(I know enoug about computers not to fall for that, so closed it, but I'm worried that even the close button could have triggered something. Antivirus hasn't found anything.
The most active link has opened another page for a few months now; google analytics with some random search, which was a bit odd but not particularly worrying.
So why is it doing this all of a sudden? All links on mumsnet seem to do it, and it has done it occasionally on facebook.
Can anyone help?
TIA

Is it just Mumsnet or other sites too (I hate to suggest this but go to netmums and see if this happens there too).

It is possible that you have a nasty. What operating system are you running (is it Windows? - if so do a google on Adaware free for your version of windows - it's a free download, install it, clean your hard drive and try again).

There is also a setting on some browsers (IE included) which opens all new pages in a new window. You can turn it off by resetting IE under your preferences.