If you read your emails and have the email client (Thunderbird, Outlook) etc. set to download pictures, then said pictures, even trivial ZERO BYTE TRACKING IMAGES can come from any address. There's a lot of prior discussions on this so I'll shortchange you here.
I commonly see these addresses on my modem history. What are they referring too? Does this mean a Yahoo email address is logging on using my internet? I do not use Yahoo. If so, can I find out the screename used? Thanks