Yahoo Mail Has Started Sending Me A Copy ????

I am running XP SP3. I am careful where I go and any funny emails received. Unless I recognise the sender its zapped.Last week 3 colleagues in a Yahoo Group posted that they had received an email from me that was either Spam or not signed as normal. I got two of the sites which appeared to be companies furthering business. I changed my password . No more since.
I run Malwarebytes,IOBIT Malware, and SAS pretty well weekly. AVG about 3/4 weeks.I did so when the above occurred.
However about same time emails I sent to the Group site suddenly started sending me a copy. I have checked my Yahoo account and I can find no reason for it. Checked my Firefox etc. I wondered if Yahoo had made changes and I emailed the Group owner asking him. He has checked and found nothing.
Today I decided to 0800 the Yahoo Support site in UK. The operator asked to connect which we did and she looked through things eventually saying that there was one good and two suspect lines into the Router.
The Router Controller was nearby and he checked and spoke with her stating its configuration. Then I was told I had too many AV programs altho I only run 3 on command and AVG on. She went into Task Manager and came up with a report log and then pointed out CRSS as a problem I have not found that to be so.
She then proceeded to try and sell me protection at $450 a year. On an aside I find this very underhand of Yahoo. But I still have the problem of the returning email copy. Its not the end of the world but because it happened about the same time as the Spam posts I am concerned that I am missing something and that the
could be some sort of virus?? on the pc. She pointed out CRSS as a trojan on a website page. However I have looked in Windows sys32 and all seems ok. I have tried to find it in Regedit without success. Can anyone give me some advice. I am not a Majorgeek or even a minor one as altho I have used pcs for a long time its all self taught.

Thank you

 

Good Day Kestrel

Thank you for your help.Im afarid old age is at play here as I remembered that I had tinkered with Yahoo account after I got the scare re spam messages sent to pals. I went back and unchecked a couple of boxes yesterday and the messages have stopped. I also ran Comodo Cleaning essentials which found a few funnies back in olf dircectories I rarely use and we killed them. So I think we have got things right as the returns have stopped and there are no comoplaints popping up.
So thank you again