Viruses Aimed at Microsoft Rise Sharply-Symantec &lt;p&gt;\&lt;/p&gt;&lt;p&gt; SAN FRANCISCO (Reuters) - The number of new viruses and\worms aimed at Microsoft Corp.'s &lt;MSFT.O&gt; ubiquitous Windows\operating system rose 400 percent between January and June from\the same year-earlier period, leading computer security company\Symantec said on Sunday.&lt;/p&gt;