Hi Helen, this problem could be caused by many things including your telephone line or modem connection but more than likely you have picked up spyware or a trojan which has taken over your computer which is now being used to relay spam whenever you go online.
Edwardquote s solution to clear out your temporary internet files is the first step (I would also clean out your Favourites as well, as the bugs often hide there too) but more often than not the bug has infected your computerquote s registry. If you donquote t have up to date security programs you can pick them up for free on the internet (however itquote s far easier to prevent an attack than remedy the problem once it has happened).
If you have no security software then I would suggest that you go on another PC with a CD writer, download / save some free security programs, copy the zipped files to disc, copy them again to the desktop on your own computer and install and run. If you have no anti-virus I would recommend the AVG Free Edition (but unfortunately itquote s being discontinued in February).
I would also recommend two freeware anti-spyware programs, Spybot Search and Destroy and Ad-Aware SE. I would not download any free software from the internet which has not been recommended as a lot of it contains spyware.