AppRiver, one of the leading anti-spam service providers, today reported a new virus outbreak on the Internet believed to be linked to spam-attacks associated with the 'back-to-school' season. The new variant of the Bagle virus is already so prevalent that it accounts for one in five viruses detected by AppRiver, which screens up to 30 million email messages each day.

Every year spammers rev up their engines with new campaigns right around the time students return to the classroom. These spam blasts are generally preceded by a virus that takes over unprotected computers and turns them into 'zombies,' or spam-spewing machines.

This year, the Bagle variant, bagle.dldr.gen, has renewed the pattern. The virus sends emails with attachments related to taxation, such as 'Work_and_taxes.zip' and 'To_reduce_the_tax.zip.'

"The Bagle virus variant went from nonexistent to the top of our list in 24 hours and currently accounts for nearly 20 percent of all viruses recognized by our systems," said Joel Smith, AppRiver's chief technology officer. "We suspect it's harvesting a fresh crop of zombie computers to be used for the yearly 'back-to-school' spam campaign."

The Bagle virus is compressed in a .RAR file containing an .exe file with labels related to taxes. These files contain executables with misleading icons. Some of the archives are ZIP files, some of them are RAR files and some of them are ZIP files with a .RAR extension.

"We suggest companies take the necessary precaution of blocking all .RAR files until the outbreak has been contained," said Smith.

The best way to prevent the Bagle virus variant from infecting your system is to make sure an anti-virus component is installed and up to date. Several companies, such as McAfee, Sophos and Norton, offer freeware or trialware components that users can install to combat viruses.