Windows OS error could come from different problems such as hardware or software issues. DOS is a denial of service attack which is a cyber attack that use a PC and a connection to flood the target server using packets (TCP/UDP). The point of such a DOS is to overload a server making it unavailable to users. DDOS on the other hand, is a distributed denial of service attack which uses several computers around the world also known as BotNet. SPAM is an unsolicited emails which try to sell you something and Phishing is a type of SPAM which actually tries to steal personal information like credit cards info, passwords and usernames.