Throughout 2010, Trend Micro published figures stating there was 1 new malware threat every 1.5 seconds. Just last week, a blogger interpreted that as being at personal risk of encountering a whopping 19,200 new threats per day (based on eight hours of online time).

Earlier today, Trend Micro upped that figure substantially, twittering that 3.5 new threats were released every second -- a 450% increase. With the wrong interpretation, some might believe that translates to an individual encounter risk of 100,800 new threats per day (based on that same eight hours of online time).

Obviously whether it's actually 1 new threat per 1.5 seconds, or 3.5 new threats per second, neither translates to actual encounter risk for users. To gauge that risk, you'd have to monitor the same user population for an extended period of time and determine what the actual number of raw encounters was at specified, regular intervals.

Fortunately, ScanSafe (now Cisco ScanSafe) has been doing that since May 2007, so we can report on the actual encounter rates. Our user population is a 15,000-seat enterprise; following are the actual numbers of malware encountered:

>> May 2007: 205 encounters
>> May 2008: 669 encounters
>> May 2009: 1,719 encounters
>> May 2010: 4,111 encounters

In other words, if you're a 15,000-seat enterprise, then you probably average 5.5 malware encounters per day. That's still a lot, but it's definitely a lot less than 3.5 every second. The moral of the story: The overall rate of new malware does not equal the overall rate of encounter.

Mary Landesman is an antivirus professional and senior security researcher for ScanSafe, now part of Cisco. In 2009 she was awarded a Microsoft MVP for her work in consumer security.