I assume it must be some kind of Malware, but I've just done a full scan with AVG, and nothing shows up.

It's just cropped up today, and it happens on Firefox (which I normally use) and on Opera (which I use quite often), but not on Internet Explorer (which I hardly ever use).

When I try a search on Google, it takes ages to load (over 20 seconds, whereas normally it comes in a flash). When it does and I type in a search, the ordinary kind of list of answers all appear - but all the addresses are to adverts. So for example if I type in Mudcat, the address which it brings up is something called "www.monstermarketplace.com/ "

Even more puzzling - when I opened up Firefox in a different account on the same machine, it still had this enormous delay before opening up, but then opened up with the right addresses. But back on the previous account the same problem, I still gett these strange and unwelcome addresses.

I've tried searching around on the net for advice, and it appears that it's a problem other people have had. But I couldn't find anywhere where the advice give was comprehensible.

I use Windows XP and have a pretty good broadband connection through Virgin Media cable. Any comments or suggestions?