In recent weeks, you've probably noticed the return of an old pest: spam. For almost two years, it seemed as if spam might finally be on the decline. Remember when Bill Gates said that by 2006, "spam will be solved"? Well, that was all going well until a few months ago when spam struck back.

According to e-mail filtering vendor Postini, spam volumes have grown 73% in the last two months. There are several recent developments that have triggered the new growth of spam:

1. Spammers are now embedding their messages in images to slip past spam filters that search for key words and phrases. The number of e-mails with images has grown from nearly zero to almost 25%.

2. Spammers are experimenting with the text in their messages, especially in the subject lines. All it takes is a few minor tweaks and a spammer can successfully go from the spam filter to the in-box.

3. More spam is being sent from hijacked home PCs, making it harder for spam filters to block so-called blacklisted senders. Spammers also are getting better at identifying vulnerable PCs they can convert to botnets, the hijkacked PCs that are sending all this new spam.

4. Spammers are turning to SMS, or text messages, as a way to target both mobile devices and PCs. This technique has proven successfull for two reasons. One, there is little in terms of security for most cell phones, making them ripe targets for spam and phishing attacks. And two, most desktop e-mail spam filters are not designed to handle spam or phishing attacks from SMS servers.

What does this all mean for you? You can look forward to lots more spam in 2007. And IT managers, this means that your spam folders are going to need more storage space, since spam e-mails with embedded images take up a lot more space.