NEW YORK: Image spam is becoming a real threat of late as spammers have found ways to bypass traditional e-mail filters that block text-based spam, say spam experts.
Some of the filters have no mechanism of knowing whether a file containing graphics can be a genuine photograph or unsolicited messages wrapped in .gif files. Many of the spammers have opted for this modality as they feel sure their unsolicited messages can slip through fooling the anti-spam filters.
According to California-based anti-spam maker IronPort Systems Inc., the use of image spam has gone up from 1 per cent of all spam in June 2005 to 15 per cent in June 2006. IronPort's senior product manager Craig Sprosts said image spam had been in decline as anti-spam filters had ways to detect it by using a mathematical formula to known spam images and creating a unique signature that software can use to detect junk. But, spammers are now using tools to automatically vary images, causing changes in the signature, thereby escaping detection.
IronPort has observed a 40 per cent increase in image spam since April received by "honeypot" accounts set up to attract junk messages for analysis.
Another anti-spam vendor CipherTrust Inc. has also reported an increase in image spam, which it said could be the result of a more efficient use of the technique or an increase in the amount of spam circulating.
Sprosts said image spam burdens e-mail systems because each message is about 7.5 times larger than regular spam. He believes its growth is helping to fuel a global resurgence in spamming.
He said much of this spam is coming from a "relatively small group of spammers with control over very large zombie networks," of hijacked computers. Spammers are estimated to be generating some 55 billion messages a day, against some 30 billion e-mail messages per day a year ago.
One of the tactics adopted by spammers appears to be to have new domains. Of the 35 million domains registered in April, as many as 32 million were never paid for and expired after five days, said Sprosts, adding many of those domains were used by spammers during the five-day free use period. This makes it difficult for system administrators to blacklist e-mail-based URLs.
