Researchers have found that Microsoft’s IP addresses were responsible for a large volume of spam to the point that they managed to top list for the US for 5 months. Microsoft topped the list in April and May for the previous year; and in March, April and June of this year.

The data is gathered by groups outside of University of Texas and the Microsoft rankings are based on data compiled by Passive Spam Block List. The SpamRankings project uses raw data about the origin of spam traffic and analyzes it to find and tracks down organizations that own IP addresses.

The Windows 8 maker hasn’t put forward any comments yet but a senior researcher at SpamRankings believes that high volume of spam could be because that part of Microsoft is MSN, which is Microsoft’s portal that includes its ISP.

Inbound spam is definitely a common occurrence and might not pose a greater risk as compared to outbound spam. Outbound spam indicates that some or all systems in the internal network of an organization would have either been compromised by botnets or some users may have been victims of phishing attacks.

The study was carried out in a bid to flag the worst offenders and to get them to improve their security. The main goals of project are to reduce spam as well as improve organizations’ security. The researchers believe that by drawing attention of companies rankings, public scrutiny along with pressure from peers and customers will force if not encourage to do something about their security.