Network Security Threats

Why network security?

When devices are connected, data can be stolen, changed or destroyed by attackers. Network security means protecting devices, data and users from such threats.

Malware

Malware (malicious software) is any program written to harm a computer, steal data or take control without permission.

Virus, worm and Trojan

A Trojan horse pretends to be a game, crack or free tool. Once installed it opens a back door for the attacker. Unlike a virus it does not copy itself.

Ransomware, spyware, adware, keylogger

Ransomware (e.g. WannaCry, 2017) encrypts files and asks for payment. Spyware collects browsing and personal data. Adware floods the screen with ads. A keylogger – software or a tiny hardware device – records every key you press, including passwords; online on-screen keyboards help against them.

How malware spreads

• Email attachments and links from unknown senders
• Pirated software, cracks and fake apps
• Infected pen drives
• Unsafe websites and pop-ups
• Systems that are never updated

Antivirus and firewall

Antivirus software scans files, detects malware using signatures and behaviour, and removes or quarantines it. Keep it updated.

A firewall – hardware or software – filters network traffic by rules (allowed ports, addresses, programs) and blocks suspicious connections.

HTTP vs HTTPS

Cookies and privacy

Cookies make sites convenient, but third-party cookies can track you across websites. Clear cookies regularly, use private browsing on shared computers and accept only necessary cookies.

Strong passwords

# A simple password-strength checker
def strength(pw):
    score = 0
    score += len(pw) >= 8
    score += any(c.islower() for c in pw)
    score += any(c.isupper() for c in pw)
    score += any(c.isdigit() for c in pw)
    score += any(not c.isalnum() for c in pw)
    return ['Very weak', 'Weak', 'Weak', 'Medium', 'Strong', 'Very strong'][score]
for p in ['12345', 'rahul2008', 'Rahul2008', 'R@hul_2008!']:
    print(p.ljust(12), strength(p))

Phishing

Phishing is a fake email, SMS or website that pretends to be a bank, school or company to steal passwords, OTPs or card details. Check the real domain before clicking.

# Spotting a suspicious link (very simple rules)
def suspicious(url):
    reasons = []
    if not url.startswith('https://'):
        reasons.append('no HTTPS')
    if '@' in url:
        reasons.append('@ hides real address')
    host = url.split('//')[-1].split('/')[0]
    if host.count('-') >= 2 or host.replace('.', '').isdigit():
        reasons.append('odd domain')
    return reasons or ['looks OK']
for u in ['https://www.sbi.co.in/login', 'http://sbi-login-verify-kyc.xyz/win',
          'https://203.0.113.5/pay', 'https://bank.com@evil.ru/']:
    print(u, '->', suspicious(u))

Safety checklist