I am new to the forum and I hope it is appropriate to begin with a request for help.
I am running windows 7 Professional on an x64 system. I have not noticed anything unusual in my computer's performance - no popups, redirects, unusual slowness or crashing.
A friend reported getting an email from my account, with my name in the subject line and a strange link as the only content. I had not sent it. I could see from the recipients list that it was also sent to a few other people in my contacts list, who would otherwise not know one another. I checked with another contact and she received a similar email with a different link included, and some different contacts in the recipient list.
I examined the header from one of these emails and saw it had a strange address in the Return-Path field. There were other details in the header that appeared odd to me, although I am not really competent to assess that.
There is no record of any of these emails in my sent folder. Nor did I receive any bounced emails, which i attribute to the alternate address in Return-Path.
I have run Malwarebytes antimalware, which found no suspicious items, Super antispyware, which found only a bunch of tracking cookies, and a Sophos antivirus scan, which found no suspicious items.
I am particularly concerned about the fact that these emails seemed to have access to my address book. Is this a likely indicator of some kind of malware on my system and how should I proceed.
Any help is very much appreciated,