Have I been hacked?

I have had Webroot for almost 10 years.  I am extremely careful on the internet.  I have all security settings high and program a full scan every morning.  In all this time only one threat (2015) has ever been detected—and quickly quarantined. I also automatically allow Webroot to keep me up to date on treats.

just recently my peer responded to an email that I sent (to a network of aprox 45 others) stating: '"You've been hacked!"

I immediately looked at my scan history and it still indicates only one threat (from 2015).  I also rescanned (deep). Nothing. He refused to tell me what the 'hack' was—only that his email indicated that my post had "malicious malware" but—understandably—had no intentions of opening it for any 'details'.  Yet—no other recipients of the same post  see anything.  Many, whom also have software that scans all their incoming mail.  Where am I going wrong here? Is Webroot somehow unaware of a malware lurking on my Windows PC.  Windows7 Home Premium ver. 6.0