Computer viruses that spread easily over the internet are currently the biggest threat to any computer. Realizing this, many technology companies have come up with robust anti-virus softwares which have been thoroughly tested by computer experts and certified with high ratings. Unexpectedly, although most of the household users have these anti-virus softwares installed on their computers, their computers are often found containing more than one serious virus threat.
Which one of the following, if true, could, by itself, adequately explain the unexpected finding reported in the passage?
A. Many household computer users are not aware of virus threats and of effectiveness of anti-virus softwares in controlling viruses.
B. With every passing year, the usage of computers in households is on a steady rise.
C. Anti-virus softwares are expensive to buy and computer buyers are often reluctant to buy them.
D. Although very effective in controlling serious virus threats, anti-virus softwares cannot catch all the minor viruses.
E. To be duly effective, most anti-virus softwares require proper installation, and most household users are not aware of correct installation procedures.