On June 7th, there was a reported case of (1) successful botnet Distributed Denial-of-Service DDOS attack. This type of attack (2) were difficult to prevent since current technology can only divert the traffic after the attack launched (3). Due to the (4) sources of attack are highly distributed, we could never monitor (5) nor stop the DDOS attack. Once the attack was launched, the affected system (6) will be unable to response to normal users.

The scary thing about DDOS is the growing size of botnet (7). With the higher penetration of broadband internet, more computers will be connecting to the Internet 24x7. If the management of these computers is not done securely, they will be a breading ground for botnet (8) and virus.(9) One area to pay special notice to is the growing trend of networked devices. Vetting machines, CD juke box (10) and other everyday electronic devices are likely to be connecting to the Internet within (11) next three to five years. These devices will have a slim OS (12) but will be able to carry out basic network activities, like ping and HTTP GET command. The sheer amount of these network devices will be a problem if the OS is not hardened.

Footnotes

1. You need "a."
2. 2. "This" is singular. Therefore, the correct form of the verb is "is" or "was."
3. You can also use "after the attack has been launched."
4. You need to insert "fact that the" or change the sentence to "Because the sources of attack…"
5. I would avoid using "nor" and use "or" instead. "nor" is normally used in conjunction with "neither" (e.g., Neither he nor she had understood the lecturer).
6. I would use "was" (past tense) because you used a past tense in the first part of the sentence. Alternatively, you could change "was launched" to "is launched" and leave "will be" there - or change "will be" to "is."
7. Do you mean "growing number of botnets" ? 8. I would add an "s" to form "botnets."
9. I would add "es" to form "viruses."
10. I would add an "es" to form "boxes."
11. You need to insert "the."
12. Insert a comma (,) before "but."