When I tried to download fresh devices' download manager as recommended by sonnet26, I got a message that there is no certificate and the software is unsigned. Does that mean someone could have gotten into my computer and be offering me hacked versions of different softwares?

Or is it OK to go ahead and download because it always says that?

If you're downloading directly from FreshDevices.com, the download should be safe. The lack of a certificate means that FreshDevices does not have a VeriSign digital signature. You are absolutely correct to be cautious.

Programs are "signed" with the signature so that the person installing the program is assured the program (1) actually originates from the alleged source; and (2) has not been tampered with (that is, altered from the original; "hacked").

There are a number of malicious websites which, when you access them, offer a bogus "upgrade" to some familiar software, such as Shockwave Flash. The downloaded program is not what it appears to be, and lacks MacroMedia's signature. Clicking "More Information" shows the program to be fraudulent.

Never install unsigned software unless you get it directly from a trusted source, either the publisher's website, or a major download site (like ZDNet, CNet's Download.com, and the like). Never install unsigned software which purports to be authored by a major publisher (Apple, MacroMedia, Microsoft, etc.), because they never release unsigned programs.