JPEG's saving as Bitmaps

Hi folks,
Just in the last couple of days I’ve been having trouble saving pictures off the web,the problem being that every time I attempt to save a jpeg it saves as a bitmap. I know the original piccy was a jpeg as it says so when I right-click on the piccy and go to properties,and just sometimes it WILL save as a jpeg but then try again 5mins later and it reckons it’s a bitmap again!
Any ideas folks?I’m a bit worried as I had a nasty virus that wrecked my last computer and the first thing it starting doing was mucking about with picture formats.I’ve done a thorogh virus scan with an up-to-date anti-virus program and it came up with nothing,which in a way is a relief but makes the whole thing more mysterious.
Any advice much appreciated…