Why should a personal computer be rebooted after new software is installed?

Email Worms Spread via email messages. Typically the worm will arrive as email, where the message body or attachment contains the worm code, but it may also link to code on an external website. Poor design] aside, most email systems requires the user to explicitly open an attachment to activate the worm, but "social engineering" can often successfully be used to encourage this; as the author of the "Anna Kournikova" worm set out to prove. Once activated the worm will send itself out using either local email systems (e.g. MS Outlook services, Windows MAPI functions), or directly using SMTP. The addresses it sends to are often harvested from the infected computers email system or files. Since Klez.E in 2002, worms using SMTP typically fake the sender's address, so recipients of email worms should assume that they are not sent by the person listed in the 'From' field of e-mail message (sender's address).