Shift in the reported number for every half a year (Chart 1) tends to decreasing.  For its instance, comparing with the number reported in the first-half of 2005 (28,265) and the one reported in the first-half of 2008 (10,993), the latest number was decreased about 60% from the past 3 years.  The major cause is that there have not been existed such virus which send a massive amount of virus mails: that is, the event which would cause significant damage is decreased.  It can be assumed that the reported number, thus, is decreased.

Chart 1: Reported Number of Virus/Half a Year

According to the detection number of virus over the past year, the number was tentatively increased from September to November 2007, subsequently the number was subtly decreased: Since March 2008, the number has been shifting in almost the same level.  W32/Looked existed in October and then W32/Stration followed in November/December 2007: they were immediately increased its numbers when they were initially existed, but the number mostly taken over is W32/Netsky unchangeably and its gross detection number is still significant.

Chart 2: Detection Number of Virus by Month

According to the detection number by virus filed with IPA, the number taken over by W32/Netsky is still significant though the reported number is decreasing.  The major viruses in the Chart 3 do not carry visible symptoms even infected and thus it is hardly recognizable by users.  Accordingly, be sure to check with or without virus in your computer using certain anti-virus software regularly even you do not see any suspicious symptoms.

Chart 3: Reported Number by Virus

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