Systems Security CHAPTER 1 9 IDS DEFENSES By implementing the following techniques, IDSs can fend off expert and novice hackers alike. Although experts are more difficult to block entirely, these tech- niques can slow them down considerably: Breaking TCP connections by injecting reset packets into attacker connec- tions causing attacks to fall apart Deploying automated packet filters to block routers or firewalls from for- warding attack packets to servers or hosts under attack Deploying automated disconnects for routers, firewalls, or servers ANTI-SPAM SPAM is also known as unsolicited bulk e-mail (UBE) and accounts for nearly 75­80% of all e-mail traffic on the Internet. SPAM is the digital equivalent of unsolicited postal mail sent by marketing companies on a daily basis across the United States. On a given day, a user is likely to receive 10 times more unso- licited ads or other unwanted e-mail messages than legitimate, useful messages. Anti-SPAM systems use a combination of algorithms and heuristics to identify SPAM based on context or even just word content. Many anti-SPAM systems also