It's pretty much a given: if you have an email account, you have spam. Lots of it. We've become accustomed to it – much like banner ads on websites - and hit the delete key out of reflex. But I was surprised at just how much of the email running across the Internet is made up of this utterly useless collection of 1s and 0s.

ArsTechnica writes that Microsoft has just released a new security report in which it categorizes 97% of email sent as junk. Though they are quick to point out that most us never see these emails thanks to server-side filtering, which has become much more effective in recent years.

If you're wondering who is responsible for this massive tide of annoying stock tips and sexual performance enhancement come-ons, the blame rests with an ever-expanding number of botnets.

These are the networks of enslaved computers that have been created through the propagation of various types of malware – typically spread through P2P services like BitTorrent.

Once activated, these botnets are capable of generating enormous amounts of spam, making them one of the most serious threats on the net today.

Yesterday, Symantec released their monthly State of Spam Report. In it, they write:

Since the shutdown of hosting company McColo in mid-November 2008, spam volumes have slowly made their way back to 'normal,'.[…] Old botnets are being brought back online, and new botnets are being created. Spam volumes are now at 91 percent of their pre-McColo shutdown levels.

Other high(low)lights from the report:

• Spammers Rethink Their Mortgage Strategy –Spammers utilize sadly familiar terms from the mortgage industry in their spamvertisements, such as the economic downturn and how to avoid foreclosure. This month’s spam report includes a list of the top 20 mortgage related subject lines.

• Conficker Used for Fake Antivirus Software Sale– Spammers capitalize on the frenzy over Conficker’s April Fool’s Day expansion date, offering the latest in antivirus security software that purportedly protects users from the Conficker threat.

• Countdown to Tax Day Continues – Do Not File the “Spam Expense”– Spammers continue to attempt to disguise themselves and dangle tax refund offers in front of unsuspecting users. This month’s spam report includes a list of the top 20 tax-related subject lines.

• “Take care about yourself!” Avoid Terror-Related Malware Spam– Spammers use ominous subject lines in that hopes that the fear mixed with the excitement might propel some recipients to disregard security consequences and click on URLs that link to malware.

As you might suspect, the best defense against spam is to install some kind of anti-spam software on your computer. If you use webmail accounts such as Gmail or Hotmail, you'll have to rely on those companies to help keep the lines of communication open and free of junk.