• You may start ending up at websites you didn't intend to go to. Your web browsing seems to get re-directed to other sites for no reason. Your browser seems to have a mind of its own. You have lost control.

• You may get alot of pop-ups showing ad's or search engines. You may get pop-ups even when you are not on the internet.

• New icons for rogue "scareware" anti-virus software may appear by the clock with lots of annoying balloon messages about how your computer is "at risk or infected with virus and trojans." In order to remove the fake threats you are prompted to "register or activate" the rogue anti-virus software.

• You may be blocked from reaching web sites to download or update anti-malware or anti-virus software. Your anti-virus or anti-malware software may either fail to start and/or produces a malware generated pop-up message and fails to start or closes after starting. 

• Your software firewall is prompting you about strange new processes that are suddenly asking for internet access.

• Any of the above are sure signs. Its all getting much more sophisticated. It's possible not to have any obvious outward signs that are noticeable but still have malware present.

       
see also tips on REDUCING your risk