E-mail - subject title Unpaid Invoice

[#1]

I have just received an e-mail claiming to be for an unpaid invoice. It, in theory, comes from 'postmasteraij@*****.bg' (I have replaced inetg with *****). I don't recognise the source. I have made the mistake of opening the invoice but that appears to be empty. It was an Excel file where the tabs at the bottom are in what looks to me like Cyrillic Script.
In case of nasties, I have run Malwarebyte, Spybot and Microsoft Security Essential, but nothing was found by them. Shall I just delete the e-mail, or should I do other things.
Sorry for being a dope.
Thanks

[#2]

I had one late this afternoon and deleted it.
It had what appeared to be an .xls file attachment but it was actually a .exe file...nasty.

[#3]

The fact that I opened the attachment - is there anything you would suggest I do to protect my pc that I haven't already done?

[#4]

I get between a few and a few hundred of these a day.
Make sure any antivirus software is up to day, do a full scan of your machine. Then download Malwarebytes, install the free (not Plus) edition and run another full scan.
Lastly you can download tdsskiller and scan for rootlkits - http://download.cnet.com/Kaspersky-TDSSKiller/3000-2239_4-75722087.html

[#5]

DomS,
Thanks for the suggestion. I had another problem a few weeks ago, where the forum helped. One of the things that came up in that was that Download.com (who are owned by CNET) was adding things to software downloaded from their web-site without telling the person doing the downloading. My question therefore is, am I adding to my problems if I get tdsskiller from where you suggest?

[#6]

Sometimes CNET add a downloader but many titles download without it.
This appears to be a better download link (direct) http://support.kaspersky.com/viruses/disinfection/5350#block1

[#7]

Thankyou DomS. I have done as you suggested, using the "support.kapersky" source. Fortunately, the scan didn't find anything
Regards

[#8]

Well known to "HoaxSlayer", I check this daily.